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MOST poultrymen know that in mature Single Comb White Leghorn females the large comb lops over on one side of the head, frequently covering the eye. The question arises, hitherto unanswered, whether the combs lop to the right or left with equal frequency. Is the direction of the lop determined by heredity? Do some combs remain erect? Are hens with combs on the left side as desirable from the economic standpoint as those with combs lopped to the right, and are either superior to hens having upright combs? Although the answers to these questions have till now been unavailable, they might be considered so unimportant that a special experiment to obtain them would hardly be justified. However, merely by recording the direction of the comb lop for the breeding Leghorns and their progeny utilized in an extensive study of genetic resistance to disease, it has been a simple matter to . . .

IN PREVIOUS papers of this series it was shown that White Leghorns differ from heavy breeds in being much more resistant to extreme heat (Hutt, 1938) and to a deficiency of vitamin B1 (Lamoreux and Hutt, 1939). It has also been stated (Hutt, 1935Hutt, 1938Hutt, 1941) that White Leghorns are more resistant to pullorum disease than are heavy breeds. This fact is so well known to experienced poultrymen that it seemed almost unnecessary to substantiate it, but, because the statement, has occasionally been challenged, presentation of some of the evidence seems desirable. This is particularly so because, even in such extensive reviews as those of Reis and Nobrega (1936) and van Heelsbergen (1929) and in the monograph of Rettger and Plastridge (1932), there is no reference whatever to the fact that some breeds are more resistant to pullorum disease than others. Roberts and Card (1935) have already reported experiments indicating . . .

1. An investigation has been conducted to determine the mode of inheritance of frizzling in the domestic fowl and to substantiate or disprove the current theory that homozygosity for frizzling is lethal. 2. Two types of frizzling, ordinary and extreme, are differentiated. 3. Incubation records failed to show any evidence of a zygotic lethal factor being operative during embryonic development. It was found that no gametic lethal factors are involved. 4. Mating of ordinary Frizzles to normally feathered fowls produced the 1:1 ratio of parent phaenotypes expected in a back cross to a recessive. Offspring from matingsinter se of normally feathered fowls extracted from matings of Frizzle x Frizzle were all normal. 5. The progeny from matingsinter se of ordinary Frizzles gave a 3:1 ratio of Frizzles to Normals and in a random sample of this population the ratio of extreme to ordinary Frizzles was as 1:2. 6. Five extreme Frizzles were tested and proved to be homozygous for the character, producing, when mated with a normally feathered male, only chicks showing the ordinary type of frizzling. 7. Eighteen ordinary Frizzles were tested and found to be heterozygous. 8. Reciprocal crosses showed that the character is not sex-linked.

The data here presented definitely establish the fact that crest, dominant white and frizzling belong to the same linkage group. It is shown that these genes have the arrangement in the chromosome of Cr-I-F with approximately 12 per cent. crossing-over between Cr and I and 17 per cent. between I and F. Since the percentage of crossing-over between Cr and F is 29, the distance in the chromosome between Cr and F, as measured by the summation of the segments Cr to I and I to F, is practically identical with that secured by directly measuring the percentage of crossing-over between Cr and F. This indicates that little double crossing-over occurs in the approximate distance of 29 units on this chromosome. In segregation of these genes in birds heterozygous for all three, no double cross-overs were recorded in 284 gametes. Evidence is adduced to support the view that cerebral hernia is ordinarily the homozygous expression of crest, but a number of irregularities were found in the manifestation of cerebral herni...

Over a period of 15 years, one strain of White Leghorns (C) at this laboratory has been consistently less fertile than two other strains (K and S) although all three have been maintained under identical conditions. The birds of the three strains are intermingled in the incubators and brooders, on the rearing range, and in the laying houses. During the breeding season, representatives of the infertile strain are given the same kinds of breeding pens as the others, and in the same buildings. Since the environment is uniform for all three strains, it is clear that the consistently low fertility of Strain C is genetically determined. From 1943 to 1953 the average fertility of all eggs incubated from cockerel- test matings (i.e., no prior information regarding the fertility of the birds used) in Strains C, K, and S was 64, 91, and 86%, respectively.

THE incidence of malpositions found in chick embryos which had died after the eighteenth day of incubation has been reported as follows: From these data, and the similar reports of other workers based on smaller numbers or on “dead in shell,” it is obvious that malpositions are largely responsible for the peak of mortality occurring during the last three days of incubation. In the representative material reported by Hutt and Cavers (1931) based on the examination of all dead embryos from 24,660 fertile eggs incubated at two experiment stations in three years, malpositions in embryos of 18 days or older were apparently responsible for 24.4 percent of the total mortality. It is obvious that to reduce the present high embryonic mortality universally encountered in artificial incubation the origin of these malpositions must be discovered, as well as some means of eliminating them or of reducing their frequency. An investigation in . . .

DOUBLU-YOLKSD eggs are familiar objects, but, so far as the writer can determine, the voluminous literature on abnormal eggs contains only two records of specimens like the one illustrated in Plate 7 (upper figure). Description. The egg was left at this department without any record of its history, and by the time it was brought to the writer's attention, the donor could not be traced. The egg weighed 71.6 grams, which is almost 20 per cent less than the 86.26 grams given by Pearl (1910) as the average weight of 18 double-yolked eggs in his collection. It resembled other double-yolked eggs in shape, but differed in being apparently truncated at the large end and showing there a dark peduncle, not unlike the stem of a pear, which protruded through the shell membranes. The latter were covered with a thin encrustation of shell. There was no air cell and no shell at the larger end other than this slight deposit on the membranes. The latter were sunken so that, when the egg was held vertically with large end upward, the surface of the membranes was slightly concave. At first glance, it seemed as if the shell at the large end had been removed, leaving only the inner shell membrane, which would have formed the base of the air cell in any normal egg. Closer examination showed that it was more likely that the large end had never had any covering of shell other than the very thin layer over the membranes. This seemed probable because (1) the normal thick shell flared slightly outward where it terminated at the periphery of the membranous area, and (2) on dissection of that part, both inner and outer shell membranes were found. If the egg had ever been completely covered and some shell then removed from the large end, the outer shell membrane would have been lost with it. When a window was cut in the shell, the nature of the abnormality was evident. In addition to a normal yolk, the egg contained another that was still enclosed in its follicle (Plate 7). It was the twisted stalk of the latter that protruded through the membranes. The larger blood vessels in the follicle were quite distinct, as was the stigma, the crescentic area free of blood vessels which normally ruptures to release the ovum from the ovary. The abnormal follicle with stalk and contents weighed only 7.4 grams. It was spherical in shape, with diameters varying from 23 to 25 mm. These figures indicate that it was

GREAT differences in the response of individuals to different diets, or to certain deficiencies in the diet, are normally expected, and are commonly assumed to result, in part, from differences in genotype. Striking results of selection for resistance to a nutritional deficiency were obtained by Serfontein and Payne (1934) when, with only one generation of selection, they were able to segregate fowls 18.6 percent of whose chicks developed “slipped tendon” (perosis), as compared with 50 percent among chicks from parents which had been susceptible to the disorder. In view of a later study by Wilgus, Norris and Heuser (1937) we may assume that much of this difference was the result of differences in genetic resistance to a deficiency of manganese in the diet. A difference between breeds in their requirement for vitamin B1 (thiamine) was later demonstrated by Lamoreux and Hutt (1939). They found that White Leghorns consistently had a . . .

INTRODUCTION WHILE there is general agreement that some degree of heterosis is to be expected from crossing different breeds, and also from crossing inbred strains of one breed, there is still much to be discovered about (1) the ways in which that heterosis may be shown and (2) the amount of inbreeding of parent strains that is necessary to induce it. This report presents some evidence on both of these points. It comes from reciprocal crosses made in two successive years between two strains of White Leghorns which, although maintained for some years as distinctly separate strains, were only slightly inbred. STRAINS CROSSED The Leghorns crossed were of the C-Resistant and K-Resistant strains which, since 1935, have been bred by the authors for resistance to leucosis and, concurrently, for increased egg production, for eggs of about 58 to 60 grams, and for a body weight of about 2,000 grams. Details . . .

THE size of the comb in different breeds bears no direct relationship to the inherited ability to live and to lay. However, within any one breed the extent to which a rather large comb might interfere with feeding or be more prone to injury could indirectly affect a bird’s health or production. Dubbing to improve a cock’s chances in the fighting pit has been practised for a long time, and in colder climates males are often dubbed to eliminate the adverse effects of a frozen comb and wattles on vigor and fertility. It is surprising, therefore, that the dubbing of females has not received consideration until recent years. Perhaps the first attempt to evaluate the effects of dubbing females was that of an unknown poultryman who reported his findings in the Australian Poultry World. These were summarized subsequently by the Editor of the New Zealand Poultry World (Anonymous, 1942). In …

Following the demonstration by Riddle and Reinhart (1) that in pigeons and doves there is a marked increase in blood calcium as the females come into laying, it has been shown by a number of workers that a similar situation prevails in the fowl. Whereas the level of blood calcium in non-laying females and males of that species is usually less than 15 mg. per 100 cc. serum, in laying fowls blood calcium is maintained at from 15 to 33 mg., with even higher levels in exceptional cases. The experiments reported in this paper were initiated in 1934 to determine the endocrine basis for this remarkable rise in blood calcium. Realizing that the rise occurs while egg yolk is rapidly accumulating in the follicles, and following the lead of Russell, Howard and Hess

Summary1. An examination has been made of 11,797 eggs which had failed to hatch, among which were 5050 embryos which had died after the eighteenth day.2. Four major malpositions of the chick embryo are described and the frequency of each given.3. It is concluded that one of these, in which the head is buried between the legs, definitely prevents hatching. In the material examined, this abnormality was responsible for 9·25 per cent. of the mortality among embryos of eighteen days or over.4. It is suggested that the other three malpositions usually result fatally, by reason of their preventing pulmonary respiration in the embryo as well as by mechanical hindrance.5. Of the embryos over eighteen days, nearly 56 per cent. were in one or another of the four major malpositions.6. Possible causes are discussed, and the suggestion made that some of the abnormal positions result from an incorrect orientation of the embryo established early in cleavage.

INTRODUCTION THE various breeds and varieties of domestic fowls, like most of those in other domestic animals, have been differentiated at the time of their establishment by characteristics of structure, size, and color rather than by variation in the physiological characters and functions by which their economic use is now measured. Association of some morphological character, or group of such characters, with a physiological one, without artificial selection for the latter. is comparatively rare in domestic animals although a number of such cases have been demonstrated in plants. The present paper reports an association between breed characteristics and an interesting psysiological character, the ability to withstand extreme heat. The unusual heat of July, 1936, in the United States caused abnormally high mortality in the human race, with deaths, for the week ending July 18, 64 percent higher than in 1935 for 86 cities with population of 37 millions 1 . Corresponding figures for . . .

DIFFERENCES between breeds in nutritional requirements were first reported by Payne et al. (1932), who observed that their Rhode Island Reds were much more susceptible to perosis than were their White Leghorns. Since then considerable evidence of genetic variation in nutritional requirements has accumulated and this has been reviewed elsewhere (Hutt, 1949). With respect to thiamine, the tests of Nichita and Iftimesco (1934) with adult White Leghorns, and those of Nichita et al. (1934) with Rhode Island Reds, indicated that the latter breed is more susceptible than the former to a deficiency of vitamin B1. This was confirmed by Lamoreux and Hutt (1939), who eliminated any possible influence of the breed difference in size by testing chicks of the two breeds instead of adults. Subsequently Scrimshaw et al. (1945) found that White Leghorns put more thiamine in their eggs than hens of the heavier breeds when both kinds are maintained …

OVULATION and the subsequent laying of a normal egg, usually within 26 hours, are preceded and accompanied by certain changes in the body of the hen. The external characters that are associated with an active state of egg production are well known and are used as the basis for the periodic culling of commercial laying flocks. By the absence of external changes considered indicative of egg production, one is able to identify non-layers and to remove them from the flock, if so desired. It is customary to consider as layers those birds which show the external characteristics associated with egg production. We have learned, however, that some birds behave as though they were laying, and show appropriate changes in body condition, without actually producing an egg. This paper presents the pertinent findings when groups of such birds were subjected to study. SOURCES OF DATA Among large populations of pedigreed White …

INTRODUCTION FOR the past ten years the junior author has been breeding fowls resistant to disease, particularly to lymphomatosis. During the course of the work it became evident that limiting factors of great importance were (1) the relatively small numbers of breeding birds that could be tested in any year, (2) the difficulty of selecting unproven cockerels that would transmit viability, and hence (3) the very small number of good, proven sires available for use in a second year or longer. When the standards set up require that the sire’s progeny must excel the flock average, not merely in viability but also in egg production, and at the same time be satisfactory in egg size, in body size and in hatchability of eggs, it is unusual to find even a quarter of the cockerels tested in one year eligible for re-use in the next. Furthermore, when the flocks under test . . .

OTHER things being equal, the amount of heat lost by a warm-blooded animal is directly proportional to the surface area of that animal. The surface area, however, is not directly proportional to the weight, but varies approximately as does weight213. This means that the surface area per unit of weight is much greater in the small animal than in the large one, and ipso facto, that in homoiothermic animals the problem of maintaining body temperature above that of the environment is more difficult for small individuals than for large ones. Kleiber (1932) calculated that if a mouse. and a steer had the same heat production per gram of body weight, and if both were required to maintain the same temperature, the mouse would need a specific insulation twenty times that of the steer. The extensive data of Wetmore (1921), including 1,558 records of body temperature for 327 species of birds, indicate that small birds maintain temperatures just as high as those of larger species. For example, the mean temperature in ten species of Paridae (tits and chickadees) was 107.90 F., exactly the same as for fourteen species of Corvidae (jays, magpies and crows). Determinations of the metabolic rates of forty-five birds representing thirty-two different species ranging in size from 0.02 to 17.6 kilograms, made by Benedict, Giaja, Terroine and others, as summarized by Brody (1932, pp. 89-97), show that in birds, as in mammals, the metabolism per unit of body weight is highest in the smallest species and decreases with increasing body size. This indicates that maintenance of high temperatures by small birds is accomplished in part by an increase in the metabolic rate. However, the amount of insulation may also be an important factor. If this be so, the greater insulation needed by the smaller birds to maintain temperatures the same as those of large ones, which are from 30 to 120 F. higher than those of mammals, might be obtained by increased length of the feathers, but the resultant disproportion between size of body and length of feathers would probably interfere with flight and hence have little 'survival value.' Since the type of feather changes little within any one order, or group of birds, it is probable that any additional insulation needed by small birds is provided by an increase in the number of feathers per unit of body surface. On theoretical grounds, therefore, there should be many more feathers per unit of area in the Chickadee weighing eight to ten grams than in the Blue Jay of about ten times the latter weight. It follows that, since the surface area per unit of weight increases with diminishing body

DURING the first 8 years of selection at this laboratory for genetic resistance to leucosis combined with other traits of economic value, it was our practice to leave each male in his breeding pen throughout the entire hatching season of 8 to 10 weeks. By 1942 it was evident that, while marked improvement had been made in the first three years, progress thereafter had been almost nil. It was equally clear why improvement had stopped. We had tried each year to find enough good proven sires to head at least 25 percent of the breeding pens. During the first 5 years, the average number of pens used for the two resistant lines together was only 13.2, but, among the 10 cockerels or so tested annually, it was seldom possible to find 3 or 4 proven sires that could be used again without considerable misgivings. In 1940 to 1942, the average …

INTRODUCTION FOUR years ago, Hutt et al. (1941) reported results for the first four generations of White Leghorns bred for resistance to disease, particularly to lymphomatosis. These showed that, whereas deaths from neoplasms during the test period were 16 percent in the unselected population with which the experiment started, in the fourth generation such deaths had been reduced to 12 percent. This decrease, really by a quarter of the original proportion, seemed significant, not merely because it was based on 785 birds, but because, at the same time, deaths from neoplasms were more than twice as frequent (26 percent) in the stock bred for susceptibility. Moreover, the decline of total mortality from 64 percent in the unselected population to 38 percent in the fourth generation permitted a higher proportion of the latter to develop neoplasms had they been genetically susceptible. The fact that only 12 percent did so is more . . .

SummaryIn an examination of 11,797 eggs which had failed to hatch, 433 specimens exhibiting teratological abnormalities were obtained.The various types of monsters observed are briefly described and the frequency of each given.The most common types were characterised by various degrees of abnormality either in the brain, cranium, or eyes, or in two of these structures, or in all three. Hyperencephaly, exencephaly, and microphthalmia constituted 93 per cent. of all the monsters observed.Other teratological abnormalities encountered included prognathia, duplicity, ectopia, cyclopia, otocephaly, malformed limbs, and absence of premaxillæ.Monsters accounted for at least 3·6 per cent, of all mortality in the material examined.Since this material included many embryos too decomposed for detection of teratological abnormality, the actual loss is probably considerably higher.No significant deviations from the normal sex-ratio were evident in any class of monsters.A decline in the frequency of such abnormalities from February to April was evident.Evidence is adduced from Stockard's experimental teratology in fish eggs, to show that a very probable cause of the production of monsters in the chick is an arrest of development of the embryo at a critical stage.Presumably such a condition results from the chilling of those eggs laid in the early stages of gastrulation.Some evidence to indicate the possibility of an hereditary tendency to produce monsters is briefly discussed.

Various studies upon the development of eggs of fowls and of pigeons have shown that the processes of formation of the egg and of development of the embryo during the passage of the egg down the oviduct are continuous throughout the twenty-four hours of the day. They are involuntary reactions. On the other hand the actual laying of the egg is a reflex for which the necessary sensory stimulus usually does not occur while the hen is on the roost at night. This means that if an egg be fully formed and ready to lay at 2 a. m ., it is retained in the uterus till the following morning. The embryo of such an egg (when fertile) would presumably have undergone some six hours further development than if the egg had been fully formed at 2 p. m . and had been laid at 2:30 p. m . Such a view is . . .

IN A PREVIOUS communication by one of us (F. B. H., 1938), it was pointed out that neoplasms caused over 38 percent of all deaths among 1,922 fowls dying during the six-year period, 1931–37, at two laying tests in New York. It was also shown that in this same population 87 percent of all deaths were caused by diseases thus far not amenable to control by sanitation, immunization, elimination of carriers, and other orthodox procedures currently recommended for the control of poultry diseases. Because of this situation, an experiment was begun in the spring of 1935 to test the feasibility of breeding strains of White Leghorns resistant to some of these diseases. A brief report of the first three years of this work was given earlier by Hutt, Bruckner, and Cole (1939). In the present paper, we present results of the first five years’ work. These include the unselected . . .

Pullo~um disease, once more graphically labelled as bacillary white diarrhoea, is a disease, primarily of voung chiclts, caused by the bacterium, Snlnzonelln pzrllorz~m. ~ f f e c t e d chiclts show symptoms within a few days after hatching and thc peak of mortality is usually passed by nvo weelts of age. Resistance is lowered by chilling, especially during the first weelt of life. Because the causative organism can be transmitted from infected hens through their eggs to the next generation, the orthodox method of control is to exclude from breeding floclts all birds that react to agglutination tests for S. pzlllorznn. Another method, unorthodox but effective, is mentioned later. Evidence that chiclts differ genetically in resistance to pullorum disease has recently been reviewed elsewhere (Hutt, 1958). I t will suffice here to state ( I ) that Leghorns have been shown to be more resistant than Rhode Island Reds and other heavy breeds (Hut t and Scholes, 1941), ( 2 ) that the natural resistance of ~ e ~ h o i n s can be enhanced by selection, as Roberts and Card (1935) have shown and (3) that equally resistant stock can be developed similarly even in Rhode Island Reds (De Volt et nl., 1941). Some yeass ago the senior author began a search for any detectable difference between birds resistant to pullorum disease and those susceptible t o it. Followino the discovery that chiclts of a resistant breed (White Leghorn) 9 are able to r a m body temperature Inore rapidly during the first 10 days after hatching than Rhode Island Reds (Hutt, 1935; Lamoreux and Hutt; 1939), further investigations showed that this samc difference distinguishes resistant chiclts and resistant families from susceptible ones within a pure breed. Eventually, from the studies of Scholcs and Hut t (1912) and Ram and Hut t (1955), recently reviewed by Hut t ( 1958), it was concluded that genetic resistance to S. ~ Z L ~ ~ O T Z L ~ J ~ is associated wit11 superior control of the thermoregulatory mechanism. That superiority is shown not only (1) by a sustained febrile reaction after infection, but also ( 2 ) , in chiclts not infected, by more rapid transition from the poiltilothermic state of the embryo during incubation to thc 1~omoiothermic one of thc ten-day-old chick. Thc ratc of that transition can be measured by thc avcragc tcmpcrature of thc chick up to 10 days of agc, or even to 6 days of dgc. I n ,211 optimum environment, the a\7erage temperature of uninfectcd chiclts at 10 davs of age is 105" to 107°F. Sincc 1,amoreus (1935) has found tcmpcratbrcs over 109°F. in adult rvactors (prcsumably infcctcd), it was recognizcd that defence in the chiclt did not lic in attaining the thermal dcath point for S. pzdlori1~17, but more liltcly in the acceleration by higher temperatures of such dcfencc mechanisms as pl~agocytosis, bacteriolj~sis and the production of anti,l~odics.

Summary1. Fertility tests of eight partially castrated cocks and three controls show that within quite wide limits of fertility and of testis size the fertility of the male fowl is not in any way dependent upon size of the testis.2. The average density of sperm suspension was found to be approximately four million spermatozoa per cubic millimetre for the thirty-six samples examined from ten males.3. The variations in the average density of sperm suspension from different birds ranged from 825,000 to over 7,000,000 cells per cu. mm., but within this range the density of sperm suspension bore no relation to fertility.4. The number of sperm per cubic millimetre of semen appears to be entirely independent of the size of the testes within the ranges covered by this experiment.5. Compensatory hypertrophy to a degree approximating to the normal weight of both testes was observed in the retained right testes of cocks castrated unilaterally on the left side at one week of age.6. Exceptions to the rule of compensatory hypertrophy included birds with subcutaneous testis grafts and two in which one whole testis and part of the other had been removed.7. It is suggested that fertility in the male fowl is dependent upon the physiological efficiency of the spermatozoa rather than upon their quantitative production.

MALPOSITION III (head under left wing) is probably the most important malposition because of its frequency, which may range up to 5 percent of the embryos still alive after 18 days of incubation, and the fact that it is almost always lethal. Its cause is quite unknown, except that it is more frequent in eggs incubated with the large end up than in those incubated horizontally (Byerly and Olsen, 1936). During examination of some 40,000 unhatched eggs it appeared to the writer that malposition III was more frequent in the larger eggs, and, since definite information on this point was lacking, an investigation was undertaken to determine the relationships, if any, between the frequencies of various malpositions of the embryo and the size and shape of eggs. MATERIAL AND METHODS During 1933 and 1934 all eggs incubated in the regular hatches at the Minnesota Agricultural Experiment Station were utilized. The . . .

Daily doses of 4 mg. thyroid iodine per 1000 and 2000 gm. of body weight proved lethal to male and female fowls. Daily doses of 4 mg. thyroid iodine per 3000 to 5000 gm. body weight caused loss in weight in males and females. The same amount of thyroid iodine to 7000 gm. of body weight caused loss of weight in a cockerel but not in a hen. Smaller doses had no effect on the weight in either sex. All doses, even 4 mg. thyroid iodine to 10,000 gm. body weight, caused hen feathering in the males. Depigmentation was quite marked in the case of the heavier doses, but less evident in that of the smaller. In general, depigmentation was most evident in the birds which declined in weight. The minimum daily dose necessary to produce marked depigmentation was 4 mg. thyroid iodine to 5000 gm. of body weight. This explains why several investigators have not obtained the depigmentation described by Giacomini and Zavadovsky. On doses of 0.8 mg. thyroid iodine per bird or less, Cole and Reid, and Crew observed production of darker feathers. On much larger doses Giacomini, Zavadovsky and the writer observed depigmentation. It would seem that the smaller doses of thyroid cause increased production of melanin, presumably by the general increase in metabolic processes, but that at a certain stage (which this experiment indicates to be around 4. mg. thyroid iodine per 5000 gm. of body weight) the production of pigment is arrested. The use of a definite dosage of thyroid iodine based on body weight has led to consistent results and to an explanation of some of the discrepancies which have previously appeared in the literature.