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There has been a great deal of controversy recently in British Columbia over the non-Canadian use of the province's recreational resources. Tourism is British Columbia's third largest industry, yet tourist facilities, especially publicly provided facilities, have been experiencing crowding problems, which many believe result in deterioration in the quality of the recreational experience. In July, 1973, British Columbia's Minister of Highways responded to this situation by advocating a ban on all United States' recreational vehicles. In the present paper the problems of recreational resource development are subjected to economic analysis. One group of non-Canadian users, namely, sport fishermen, is singled out for attention. The consequences of various relevant recreation policies are discussed on a regional basis, drawing on a selection of studies undertaken by the Northern Economics Unit, Federal Fisheries Service, in Vancouver. The conclusions of the paper are as follows. It is evident that public attitudes towards non-resident use of locally identified recreational resources vary significantly from one region to another. Overcrowded conditions prevailing in some areas are not evident in others and policies must be flexible enough to take account of regional variation. Furthermore, excess demand is often a reflection of inconsistent government policies which produce a gap between the planned utilisation and the planned provision of facilities. Under such conditions discrimination on the basis of residential status is likely to be carried to lengths beyond those justified by economic analysis. In particular, in the case of British Columbia, to focus attention on restricting non-Canadian use is to divert attention away from the real problem. In the final analysis, if governments are concerned with providing an optimal amount of good quality recreational opportunities and maximising the real net benefits accruing to residents under their jurisdictions, then a policy package more finely attuned to these objectives is necessary.

In 1971, the Model Cities Program subsidized 25,000 jobs in municipal and nonprofit agencies. Both the original legislation and subsequent administrative rulings require participating cities to give preference in hiring to residents of the target areas-the urban ghetto. Yet, by the spring of 1971, fewer than half the positions were held by ghetto residents. Moreover, nonresidents were being paid significantly higher salaries than residents. This paper attempts to identify the determinants of intercity variation in "resident participation rates" and the causes of the resident/ nonresident differences in earnings. It was found that cities with highly structured bureaucracies and/or strong mayors allocate a larger share of Model Cities jobs to "outsiders" than is the case for other cities. On the other hand, real or potential "black power" (as measured, for example, by whether or not the city experienced a major civil disorder in 1967) increases ghetto participation in the Model Cities Program. Analysis of more than 14,000 individual employee records shows that neither occupational "crowding" nor lack of educational credentials sufficiently explains the salary differences between ghetto and nonghetto Model Cities workers.

Space was reduced from 9.3 to 2.3m 2 /cow during wk 2 and 4 for a group of 17 cows in a 4 wk study. Dominance rank was estimated from observation during 9 previous and 4 current wk. Leucocytes were determined from weekly quarter samples. The lot was marked into 5.9m 2 squares. Cows were observed during three 1h periods following feeding for each lot size. Cows with 2.3m 2 /cow entered fewer squares and had fewer herdmate encounters. Cows low in dominance rank moved about more than dominant herdmates as the correlation between dominance rank and squares entered was .33. Lot size did not affect daily milk yield. Cows at 9.3m 2 /cow had higher leucocytes than at 2.3m 2 /cow. At the end of this study six cows were singly isolated 24h in a holding pen 1.8×2.3m. Feed and water were provided. Milk yield was not affected. Leucocytes in samples taken initially and at 6h intervals during isolation increased generally but not significantly above the mean for 13 wk previous.

Mice were undernourished by rearing in litters of 20 pups per mother, weaned onto stock diet and their shuttle-box avoidance performance measured at 2 months of age. The mice from these large litters learned the avoidance response more slowly than controls (mice reared in litters of 5). In a second experiment, avoidance performance was measured after nutritional rehabilitation until 2, 4 or 6 months old. No significant improvement was observed in the previously malnourished mice. In the controls, performance was high at 2 and 4 months but by 6 months had fallen almost to the same level as the test group.

Despite widespread belief that psychosocial processes may be important in disease etiology, attempts to document the role of such factors in epidemiologic studies have led to conflicting and often confusing results. It is the thesis of this paper that this is largely a result of inadequacies in our theoretical framework. The point of view is presented that this stems from an uncritical subscription to and often erroneous interpretation of “stress” theory, a failure to recognize that psychosocial processes are unlikely to be directly pathogenic (in the way that, for example, a microorganism is) and unlikely to be unidimensional. An alternative point of view with data from animal and human studies is presented, and the implications for research strategy and the delivery of health care are discussed.

Benjamin C. Marsh, a vigorous young social worker in the early years of the twentieth century, attacked the extreme congestion of poor people in the nation's largest cities. In his analysis of the causes of congestion, Marsh identified the basic dynamics of large-scale crowding and offered some of the most radical solutions of taxation, land-use, and planning proposed during his day. As an early leader against the overcrowding of land, the author of the first book devoted entirely to city planning, and the founder of the first National Conference on City Planning, Marsh's career points up the diversity of style and ideology that characterized the pioneers of the planning profession.

Reptiles display a diversity of behavior that is reflective of their evolutionary heritage from fish and amphibians and their ancestral contribution to the diversity found in birds and mammals. Much of the behavior observed in reptiles seems specific to the ecological setting within which they live. As a result, a diversity of behavior is found in each of the groups of modern reptiles. Recent studies on the social behavior of lizards have proved them capable of a variety of behavioral postures, sequences, and sociality that exceeds that found in some mammals and birds. While many species of lizards are territorial, others are hierarchial and some have harems. For all those territorial species studied, crowding results in increased social interaction, increased aggression, and a switch to hierarchial behavior. While smell and sound may be important stimuli for social behavior in some reptiles, posture, actions, and especially color appear to be most important in diurnal lizards. Temperature and energy studies suggest that the large extinct dinosaurs probably fought considerably less than commonly portrayed in movies and stories, but were also probably much more brightly colored than commonly shown in reconstructions.

Japanese quail, housed one to a cage, were exposed to reduced living areas caused by an accumulation of their own eggs. After an average of 14 eggs had accumulated, these birds began to destroy their eggs at the same rate they laid them. The effect was to maintain about .026 m.2 of clear floor area. No changes in egg production were found. Behavioral control of living space is suggested by these results.

T he orthodontic literature abounds with speculation on the etiology of incisor crowding as a late (postpubertal) growth phenomenon. Lombardil cites most of the prominently considered factors in his survey of the literature: tooth discrepancies, arch size, interference of canines in lateral excursive movements, overbite, overjet, tooth removal, incisor-mandibular plane angle, type of original occlusion, third molars, and muscular forces. In their growth studies Bj6rk,2 Subtelny and Sakuda,3 and van der Linden4 report or present data revealing lingual uprighting of the incisor segments during late growth. Weinstein,5 citing Bjijrk’s study, speculated on the possible etiologic role of this uprighting in incisor-segment crowding during the typical postorthodontic-treatment growth period. LundstrijmG mentions the possible role of net lingual crown movement of the anterior teeth in decreases in arch circumference. The present study is a mathematical investigation of incisor uprighting, conducted in two parts. In the first part a mathematical method is derived to serve as a vehicle for the interpretation of and correlation between the data available from two growth studies, those of Sillman’ and Bj6rk.2 The method is used to predict the anterior crowding to be expected from the changes in mean anterior arch dimension reported by Sillman during a postpubertal growth period. The changes in mean incisor axial inclination during late growth reported by Bjiirk arc then related to the changes in mean anterior arch dimension of Sillman to determine the possible contribution of the former to the latter. The above investigation is based on mean dimensions and can therefore provide only a typical indication of the actual events. Therefore, the second part of the

Eight years of annual camping participation data, reported by a panel of 459 camping families, revealed that 51 percent of the campers were either camping less or had dropped out of the camping mar...

Various processes leading to crowding are identified, and the diagnosis, prevention, and treatment of three types of crowding are discussed. The morphogenesis of teeth, the development of the dentition, and the growth of the craniofacial complex are discussed in relation to the origin of crowding. The diagnosis, prevention, and treatment of three different types of crowding are discussed.

Crowding factors are those substances released by fish, which, under crowded conditions, inhibit both their growth and reproduction and depress their heart rate. We have partially purified the crowding factor from goldfish and carp by following a heart-rate-depression assay. The heart-rate-depression activity eluted with the diglyceride fraction from both silicic acid and Sephedex LH-20. A slightly different activity eluted with the free sterols. The peak activity associated with the diglycerides has a distinctive ultraviolet spectrum distinguishable from that of phthalic acid esters, which are also active in the assay sytem and are found in fish tissues and fish water.

This paper gives initial results of a field study of the Black Swan to investigate the hypothesis that aggression functions to space out individuals over a resource. Spacing-out is designed as one bird increasing or maintaining the distance between itself and another. Probably aggression is usually connected directly or indirectly with a resource such as food or water. Among feeding swans aggression is common and increases as the flock increases but probably does not space out individuals over the food. Rather, there appears to be direct competition for food either for short-term individual gain or for long-term adaptive gain. At high densities the situation changes and the resource only indirectly influences the occurrence of aggression in so far as it causes crowding. A scarce resource leads to crowding and the reduction of individual space to a minimum. Aggression maintains that individual spare and thereby spaces out individuals over the resource. In such situations aggression is motivated primarily by factors internal to the individual and not by external actors connected to the resource. Internal factors also influence the occurrence of aggression in feeding flocks and cause highest occurrences when the birds are most hungry.

SummaryThis study was an attempt to induce hypertension in rats by the continuous psychosocial stimuli caused by aggregation. Wistar rats of both sexes were isolated from weaning to 4-5 mo of age. Tail cuff pressures were obtained every other week during the last 2 mo of isolation and up to 8 weeks of aggregation. Two types of physical conditions were used for aggregation: (1) 6 interconnecting cages in a wheel-like arrangement around a central eating and drinking area; (2) a single cage. Two wheels were used each with 24 rats, 12 males and 12 females and 10 single cages, each with 2 or 4 rats of the same sex. Other rats of both sexes remained isolated as controls. Approximately one-third of all aggregated rats of both sexes showed a 15 mm Hg or more average increase of systolic pressure during aggregation; other aggregated rats showed less average pressure rise. Rats in single cages did not fight nor did wheel aggregated females; nevertheless, arterial pressure increased among these rats. Among wheel agg...

In our country it is now often written that documentary matter is crowding and almost crowding out the literature of imagination [vymysel — also invention or fiction]. S. S. Smirnov has said that life in recent decades has provided completely unusual material which the richest fantasy could not possibly have created. Maia Ganina says that the future belongs to the documentary or to brilliant imitations of documents. Finally, one popularized work on aesthetics explains that the most fruitful trend in the development of realistic literature is precise reproduction of an actual event, in which the author's imagination is totally absent from the story. (1)

The City is a civilizing influence. This is one of the enduring themes of western thought. The crowding, filth, and exploitation of the industrial city in nineteenth-century Europe could not dampen the enthusiasm of urbanists such as Weber, Ruskin, or Spengler; nor is there any dearth of eulogizers of today‘s sprawling megalopolis. This mode of thought has also found its way into the poor countries of the third world, where the overwhelming majority lives in isolated villages. The current message for them is to seek urbanization if they want to be prosperous. This is the essence of a now familiar proposition that cities are necessary for economic development.

A locomotor activity study in 6 strains of male mice indicated that the BALB/c strain ranked lowest and the C57B1/6 strain ranked highest in locomotor excitation after treatment with d-amphetamine. A further study comparing only the BALB/c and C57B1/10 strains again showed a significant interaction of drug and strain effects. Additional significant determinants of motility were lighting and social condition during test (1 or 4 mice). Lighting (dark, dim and full light) also interacted significantly with drug, strain and grouping effects. Whereas the C56B1/10 mice showed higher levels of motility, the BALB/c showed the greater absolute increases in motility following amphetamine. The BALB/c strain also showed greater lethality under aggregated conditions (group of 10 mice) in the dose range used for activity studies.

SUMMARY Groups of 8 pigs were housed at 0 · 56 (high), 0 · 77 (medium) and 1 · 19 (low) m 2 per pig. Feeding, drinking and dunging facilities were equal for all treatments. Liveweight gain and voluntary food intake were adversely affected on the High stocking rate compared to the Medium and Low stocking rates. Efficiency of food conversion was not affected. Pigs on the High stocking rate spent more time eating and less time sleeping when compared to pigs on the Medium and Low stocking rates for some replicates. Pigs on the High stocking rate visited the drinker less frequently than pigs on the Medium stocking rates. Peculiarities in maintenance activities are discussed.

A laboratory experiment was conducted in which groups of Ss performed simple and complex tasks for one hour in three conditions of crowding: (1) noncrowded, (2) crowded, (3) crowded-with-perceived-control. Immediately afterward, all groups worked in a noncrowded situation on two additional tasks, one involving frustration tolerance and the other involving quality of proofreading performance. Conditions of crowding had no effect on simple or complex task performance. In the postcrowding situation, however, significant negative behavioral aftereffects were observed for the crowded groups on the frustration tolerance measure, though perceived control ameliorated these aftereffects. There were no significant aftereffects on the prooofreading measure.

Summary The life-history of Schistocerca pallens (Thunberg) has been studied under controlled laboratory conditions. Both isolated and crowded stocks passed through six nymphal instars, with which the number of eye-stripes in the compound eye correspond. The mean length of nymphal life of isolated individuals was 64·8 days for males and 67·1 days for females. Mean duration of nymphal life of individuals reared in crowds was 60·1 days irrespective of sex. The mean time elapsing between the last ecdysis and the first oviposition for isolated females was 32·8 days. Each female laid an average of 6·36 egg-pods with an average of 57·8 days. Each female laid an average of 6·36 egg-pods with an average of 57·8 eggs por pod; of these 63·3% hatched. Crowded females laid their first egg-pod on the seventeenth day. They laid an average of 14·44 egg-pods per female with a mean of 60·70 eggs per pod, of which 77·58% hatched. There was no significant difference in fecundity between females grown at the two rearing dens...

1. 1. Captive redpolls maintained under constant conditions of light and temperature and fed three diets with different fatty acid compositions deposited the same composition of fatty acids in their depots regardless of diet. 2. 2. The depot fat of wild caught redpolls which were feeding on a natural supply of Chenopodium seed during migration contained over 80 per cent linoleic acid, three times as much as the captive birds, and twice as much as wild redpolls in the breeding season. 3. 3. It is suggested that the environmental conditions of photoperiod, temperature and captivity and the physiological state of the bird (migration, breeding, etc.) exert a greater affect on the fatty acid composition of the birds' depot fat than does diet per se .

T HE relative significance of genetic and nongenetic factors in crowding an11 spacing, according to investigations that I have performed on 202 pairs OS twins,4 is shown in Fig. 1. Genetic and nongenetic factors seem to have about the same influence, perhaps with some preponderance for the former. (Clearly, it is no simple matter to decide, in the individual ease, whether crowding that appears after premature loss of deciduous teeth is due to this loss or wbethtr a coincident hereditary influence is, in fact, responsible. Even if the crowding is localized to the second premolars, it cannot be excluded that, as such, it is genetically determined and that only its localization and degree arc ascribable to the premature loss. One difficulty in deciding the effect of early loss of deciduous teet,b relates to the fact that tooth migration after such loss may be of a temporary nature. Rather extreme cases of this type have been published by Kantorowicz” and Seipel,7 showing how a considerable loss of space occurring during the shedding period can be regained on eruption of the premolars. In order to ascertain the final effect of premature loss of deciduous teeth, it is necessary, therefore, to follow the case to the end of this period. Systematic investigations of the relationship between premature loss aml subsequent crowding of the teeth have been made by several workers, for some of which the size of the case series and the age at the final observation are given in Table I. TABLE I

The study of animal aggregations during the past few years in this and other laboratories has uncovered a large group of interesting and valuable facts concerning the reactions and relations of animals when placed with others of their kind. This body of data has recently been reviewed by Allee ('31). Evidences of a "group effect" have been based upon such things as growth, reproductive rates, survival under toxic conditions, and other similar indices. In the fishes there has been some work on the effects and causes of aggregations. Church* ('27) has shown that the growth of certain tropical fishes is conditioned to a considerable extent by the number of individuals present in the aquaria. The retardation of growth when larger numbers were present was ascribed to the presence of accumulated excretory products. Other workers have come to the same conclusions concerning the effects on growth produced by crowding of fishes (Willer and Schnigenberg, '27; Kawajiri, '28). Much of the work on fish aggregations has dealt with species which ordinarily form schools in nature. Such aggregations seem distinctly different from the vast majority of fishes which do not appear to have the " schooling instinct." An interesting problem presents itself in bridging the gap between the solitary forms and those which exhibit highly integrated mechanisms of aggregation. It was thought probable that even in fishes which show no schooling reactions but which tolerate the nearby presence of other fishes there may be some measurable physiological effect of grouping or crowding other than the effects of growth, knowledge of which would open the way to further investigations upon the general problem of aggregations. Such effects have already been reported. Welty ('30) has shown that in goldfishes, which have not been considered as social, there are differences in learning behavior according to whether the fishes are single or in groups. Thus, it may be that even in animals which have hitherto been thought of as non-schooling, or non-social, there are influences producing effects which have so far been either overlooked or neglected.

SUMMARY Both crowding and poor nutrition induce the appearance of emigrants in Rhopalosiphum padi L. No emigrants developed when the aphid was reared in isolation for six successive generations on actively growing leaves of bird cherry. However, emigrants developed as soon as the leaves ceased to grow or when the aphids became crowded. Crowding of mothers and postnatal crowding of the nymphs of apterous exules both influenced the induction of alate exules. The highest proportion of alate exules developed when both mother and offspring were crowded. Short day-length induced the appearance of gynoparae and males. For 50% production of gynoparae and males, over the range of temperature 10–18dC, a 1.75 h reduction in day-length is required for every 4d increase in temperature. At 18 dC, even at day-lengths as short as 6 h, exposure for three generations is required before all offspring become gynoparae or males. Low temperature and short day-length was ineffective in inducing the development of gynoparae or males in the first three generations developing from the fundatrix.

WITH the trend of modern medicine toward increasing emphasis on the patient's r6le as participator in treatment, and the consequent need of studying the patient from all angles of his personality as a basis for medical care, it becomes highly important that the nurse who has the day by day contact with him should be prepared for an even more socialized type of nursing than has previously been conceived. Along with this development in medicine has come, too, a crowding of the nursing school curriculum which makes difficult the addition of other courses. The curriculum of the National League of Nursing Education has for many years included among others outlines of courses devoted to the social aspects of nursing, but selection has had to be exercised by the individual school in planning its curriculum. This necessity for selection has, perhaps, explained why so little time, comparatively speaking, has been given to the consideration of the recipient of medical and nursing care in contrast to the care itself. These two developments, the infiltration of medical study and treatment with recognized and articulated social concepts and the need for the fullest possible use of the time allowed in the curriculum, help to determine the suggested plan for introducing these social concepts to the student nurse. They indicate the advisability of considering the plan largely as an approach, an attitude, or a point of view, instead of as a definite addition of subject matter to an already overcrowded curriculum. Even though a beginning plan may consist largely of adaptations of already existing courses, a relatively small amount of formal instruction, perhaps a separate course, devoted entirely to the social elements of nursing will help the student nurse to find meaning in these adaptations. As a working guide for the formulation of the social component of the nursing school curriculum, the following objectives may be used

A number of specific criticisms are made of Gray's theory that female rodents are more fearful than males: first, measures from the tests he cited are not related in a way which is adequately described by a unitary concept; secondly, sex differences in ‘fear’ measured by these different tests are not controlled by the same set of hormonal factors in each case; thirdly, sex differences in open field measures are more variable than Gray suggested; fourthly, an alternative view of sex differences in avoidance conditioning is presented, which accounts more adequately for recent work involving sex hormones and which is difficult to explain using a ‘fearfulness’ hypothesis; fifthly, alternative explanations are presented for inferences made from sex differences in corticosterone levels, and in response to crowding. More general criticisms are made of the inferences Gray, and Gray and Buffery made concerning the adaptive significance of sex differences, particularly with regard to ‘fearfulness’. Certain crucial assumptions of their theory are questioned: (1) that hormonal effects on behaviour are most usefully considered in terms of major motivational variables; (2) that all hormonally-produced sex differences are the result of direct effects of the hormone on the CNS; (3) that such sex differences are relatively fixed genetic characteristics; (4) that ‘dominance’ and W YNNE -E DWARDS ' (1962) theory of population control can provide an adequate foundation for a general theory of sex differences.

There are numerous environmental variables which directly and independently effect the growth rate of tadpoles. The principal factors are, (1) temperature of the medium, (2) amount of available food, (3) amount of radiant energy through light, (4) amount of surface and available oxygen, (5) amount of accumulated excretory wastes, (6) amount of bacterial growth, (7) amount of available volume per individual, (8) amount of available space per individual, (9) amount of forced or stimulated exercise, (10) presence of growth inhibiting substances, X-substances, or autotoxins. In any experimental work involving tadpole growth rate, all of these variables must either be eliminated or controlled. Of all of the variables listed above, the space factor has not been adequately recognized or evaluated in respect to aquatic forms. According to Allee ('31), Hogg ('54) was the first to note the limiting effect of volume on the growth rate of aquatic forms; Semper ('74, '81) suggested that this retardation of animal growth might be due in part to the mechanical disturbances conditioned by crowding; DeVarigny ('94) suspended glass tubes measuring 2 to 3 cm. in containers of various sizes, the tubes being closed over the bottom with muslin. In each tube he placed a single specimen of Lymnamea stagnalis and concluded from results that the growth variations depend on total volume, surface area, and the accumulation of faeces, rather than space. Crabb ('29) stated that food, foul media, and crowding all effected the growth rate of these pond snails. In respect to the tadpole, with which this paper is concerned. Yung ('85) stated that the dwarfing of tadpoles in crowded conditions was due to insufficient aeration; Bilski ('21) found that frequent changes of water or crowding would retard the growth rate of tadpoles of Bufo and Rania esculenta. A corollary to crowding is an increase in the number of frequency of contacts, and it was to this stimulated exercise that Bilski attributed retardation in growth rate. On the basis of these observations, and those of Semper on snails, Bilski devised the following formula to express growth as inversely proportional to group stimulation (see Allee, '31, p. 115, for derivation)

To evaluate the concern that "non-emergent" patlents are Inappropriately crowding emergency facilities the level of sensitivity to a list of symptoms was determined for 522 patients utilizing an emergency department. Patients selected those symptoms they regarded sufficiently serious to warrant medical consultation. Using the attitudinal scale of Hetherington and Hopkins, the selections permitted classifying patients into one of three groups: hypersensitive, sensitive, and insensitive. Sensitive patients appropriately recognized the medical significance of symptoms. Insensitive patients thought serious symptoms were trivial while hypersensitive patients felt trivial symptoms were serious. The majority, 55%, were found symptom insensitive. Only two were sensitive to symptoms. Relating the three categories to characteristics of the patient population, patients with "non-emergent" conditions, lower social class, and those without other physician contact were found more frequently symptom insensitive, ie , less capable of properly identifying serious symptoms. Also more insensitive to symptoms were those either referred by their physician, or living close to the hospital, or arriving during the 18 hours between noon and the following day at 6 AM. Insensitivity predominated for patients of all ages and sexes except for women in the 20 to 34 year range, who were hypersensitive. More patients were hypersensitive on Monday and Friday than on other days. On all days, more hypersensitive patients arrived between 6 AM and noon than at other times. Contrary to the popular view, patients utilizing an emergency facility are not generally hypersensitive to symptoms. They more frequently deny than overemphasize illness.

As the result of a previous investigation, involving the analysis of environmental factors controlling population increase in nature, it became apparent to the writer that population density constituted an environmental factor which had been comparatively neglected, doubtless on account of its obscurity, but whose effects were nevertheless of greater significance than generally realised. It seemed desirable, therefore, that this relatively obscure phenomenon should be investigated, and the writer commenced work at the Laboratory of General Physiology, Harvard University, U. S. A. It has long been known that crowding of animals produces definite and peculiar effects on the various vital processes, and even the morphology of the individual. For instance, as far back as 1854, Hogg produced evidence to show that a snail kept in a small cell would only grow to such a size as would enable it to move about freely. Later, Semper (1874) came to the conclusion that there was a relationship between volume and the ultimate size of the individual. As regards the effect of crowding upon reproductive rate the first observation appears to have been made by Balbiani (1860), who reported that Paramecium must be placed in not less than 2-3 c. c. of medium to bring about maximum productivity. Again, Farr (1843) showed that there existed a definite relationship between the density of the human population and the death-rate, and anticipated the trend of modern biology to the extent of elaborating a mathematical formula which conformed to his findings.

One of the major objectives of modern ecology is analysis of the role of ecological processes in the evolutionary origin of adaptations. The problem of the origin of migration, however, has received little attention from this standpoint. Even for birds, in which the phenomenon of migration has been a major focus of research, most attention has been directed to the study of proximate factors important in initiating migration and the physiological processes and orientation mechanisms involved in the actual movements. Few studies have concentrated on the ultimate factors responsible for the origin of these complex mechanisms. General theories of the evolutionary origin of bird migration have been in existence for a long time. Thomson (1926) and Lincoln (1939) have summarized early theories, which' tend to fall into two main groups: (1) northern ancestral home theories, and (2) southern ancestral home theories. Northern ancestral home theories assume that most presently migratory forms were permanent residents in preglacial northern areas corresponding approximately to their present breeding ranges. With advance of continental glaciers and attendant climatic changes these birds were forced southward, from where they either attempted to return yearly to breed as close to their ancestral home as possible, or in some way retained a racial memory of the ancestral home, to which they were able to return seasonally following glacial retreat. It is often suggested that the stimulus for these return movements is the crowded conditions created in tropical and subtropical areas due to the northern birds being forced south. Southern ancentral home theories assume that most present migrants were originally permanent residents in southern areas, possibly corresponding to their present winter ranges. Following glacial retreat these species began to invade seasonally favorable northern areas for breeding as a result of competition for food or breeding sites in southern areas. Some authors (Berlioz, 1950; Dorst, 1961) have suggested the operation of both of the above patterns. Although these ideas have received extensive criticism (Mayr and Meise, 1930; Wolfson, 1948; Moreau, 1951) they have found their way in almost unmodified form into some recent textbooks of ornithology (Wallace, 1955; Welty, 1963). Mayr and Meise (1930) have suggested that the existence of areas with seasonally favorable and unfavorable conditions, rather than the occurrence of glaciation, is the condition required for the evolution of migration. They suggest that the normal reproductive excess, primarily through competition for food, is the factor favoring development of mechanisms allowing seasonal occupation of such areas. Although recognizing that migration must thus have existed in preglacial times, they conclude that, due to the great restriction of migration routes which must have occurred during glacial maxima, modern migration route patterns are almost entirely post-glacial in origin. They show that extreme crowding of birds in tropical and subtropical areas during glacial maxima is unlikely, and hypothesize that changes in distribution patterns and migration routes during glacial advances and retreats are the results of extinction of local populations and dispersal resulting from normal reproductive excess. Intraspecific competition and intensification of migratory drive are suggested as factors important in the elongation of migration routes and the origin of "leapfrog" patterns in which races breeding farthest north winter

Melanoplus sanguinipes (F.) females arising from crowded parents lived longer and produced more eggs per pod and more pods per female than those from uncrowded parents. The increase in eggs per pod persisted into a 3rd generation although to a lesser degree. The number of ovarioles did not differ but females from uncrowded parents weighed about 30% more than those from crowded parents. Descendants of crowded parents produced almost twice as many eggs as did those from uncrowded parents. This provides an explanation for the rapidity of buildup of non gregarious economically important grasshoppers under favorable weather conditions.

1. A method has been described by which it is possible to scatter isolated tissue cells in a suitable medium. 2. Experiments were undertaken to determine whether minute fragments of fibroblastic culture are able to persist and multiply when transferred into a new culture medium. 3. Cell divisions were not observed in isolated cells under the conditions of the experiment. Growth took place only when the tissue cells were numerous and close to one another.

1. 1. Third molar agenesis, spacing and crowding of the dental arches, and mesiodistal crown diameters of the lower right first molars were investigated in 195 caries-free white male naval recruits, 17 to 25 years of age, by means of stone study models and roentgenograms. 2. 2. In 25 per cent of the men one or more third molars were congenitally missing. 3. 3. In general, the maxillary teeth were more frequently spaced and less frequently crowded than the mandibular teeth. Only 11.3 per cent of all the men studied had perfectly aligned dental arches (no spacing or crowding in either arch). 4. 4. When third molars were congenitally missing, the teeth in both arches were more frequently spaced and less frequently crowded, and the mean mesiodistal crown diameter of the lower right first molar was smaller than when no third molar agenesis had occurred. 5. 5. The foregoing relationships were most pronounced when all four third molars were congenitally missing. 6. 6. The relationships of third molar agenesis to reduction in tooth number and tooth size were discussed with a view toward their possible association with spacing and crowding of the teeth.