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Many of the subjects about which biologists disagree concern the interpretation of function. Morphological, physiological and behavioral characters can simultaneously serve several various functions, all of which are subject to natural selection. These may operate synergistically, but when two produce opposing effects, the one possessing the greater survival value at the time is selected. Often a compromise between several different evolutionary functions results. When the functions under consideration are viewed from a wider angle, a synthesis between differing opinions can sometimes be achieved and a greater understanding of the phenomenon obtained. It should be remembered that, even if an adaptation is invoked for only a brief time during the life of its possessor, it might well be selected merely because of its transient value then. This contribution is not a review, nor is it concerned with the biochemistry and physiology of pigmentation. Rather, it is a discussion of some of the diverse functions that have been ascribed to animal colours. A few typical examples are considered, chosen mainly from among tropical animals including human beings.

While Saudi Arabia has recognized the dangers of uncontrolled hunting and has introduced conservation measures in its own territory, prominent members of that kingdom are killing large numbers of game, including endangered species, in neighbouring countries. In this report the author presents evidence of the devastation caused by Saudi hunters in the Sudan. While the latter country has outlawed hunting, enforcing the law against Saudi nationals is fraught with difficulties.

SYNOPSIS The occurrence of trans-hex-2-enal in secretions of the stink gland of Piezodorus teretipes is described.

Spiders (Araneae) and scorpions (Scorpiones) are two orders of the class Arachnida, subphylum Chelicerata. In addition to ticks and mites (Acari), the Arachnida also include whip-scorpions (Thelyphonida), tailless whip-scorpions (Amblypygi), wind-scorpions or camel-spiders (Solifugae), false-scorpions (Pseudoscorpiones), harvestmen (Opiliones) and some other less important orders. None of these minor orders has any medical significance. Larger Solifugae are alleged to give very painful bites, but this is a most unusual occurrence and these arachnids are not venomous; Mastigoproctus giganteus, the vinegaroon of southern USA and Mexico and the largest of the whip-scorpions, ejects a defensive spray from a movable knob at the base of its flagellum that can blister sensitive human skin and stain the fingers but in other respects the species is harmless.

By means of aktograph apparatus, immature specimens of A. avicularia have been shown to be crepuscular, with a weak bimodal rhythm of locomotory activity. The peak at the subjective dusk is more pronounced than the one at the subjective dawn. These spiders are “sit wait”; predators and their activity is limited. They are less active, and have a weaker circadian rhythm, than desert‐dwelling tarantulas. This supports the hypothesis that large desert‐inhabiting arthropods are generally both more active and show more marked rhythmichy than tropical forest species.

Rates of water loss in dry air at room temperature (21±2°C) have been measured from seven species of forest-dwelling mygalomorph spiders. They range from 0.260% body wt h−1 in the tube-dwelling trapdoor spiderDyarcyops sp. (from the humid coastal regions of eastern Australia) to 0.030% wt h−1 inBrachypelma smithi (from drier environments in Mexico). There is a tendency for rates of transpiration to be related to the humidities of the spiders' normal environments and micro-habitats.

L. festiva is able to exist in the hot, arid, Sahel savanna regions of Africa in consequence of its nocturnal circadian rhythm of locomotory activity, and its low rate of water loss during periods of inactivity when an epiphragm has been secreted and while the snail is aestivating.

Woodlice are easy to obtain in large numbers, their biology is relatively simple, they are easy to culture, and the common species can usually be recognized with the naked eye: consequently they provide ideal material for student research projects. Various aspects of their distribution, including the influence of soil pH are discussed. Investigations of the effects of wind speed on nocturnal activity, and methods to be employed in population studies are described. The dearth of field observations on predators and parasites is also stressed. By means of physiological investigations on transpiration, combined with choice-chamber and aktograph experiments on behaviour, it can be shown that water conservation provides a unifying theme for many inter-related aspects of the biology of terrestrial isopods.

The results of aktograph experiments suggest that S. gregaria is primarily day‐active although its circadian clock can, to some extent, be synchronized by changes in both light and temperature. Low temperatures exert a threshold effect on activity. The nycthemeral rhythm of the desert locust is feeble in LD 12:12, even with fluctuating temperatures. This, is probably of adaptive significance. It certainly accords with the plastic and opportune nature of locust behaviour, upon which survival depends under the unpredictable conditions of the desert climate. For the insect must always be ready to exploit temporary and irregular amelorations of its harsh, arid environment. The desert locust, therefore, cannot afford to adopt rigid rhythms or behaviour patterns that might cause it to lose the benefits of a chance shower or to miss the temporary appearance of green grass. It is argued that the persistence of a rhythm fora short while could be due to an endogenous ‘clock’ or to an exogenous periodicity ...

The day time periods of activity of Gazella dorcas dorcas L. in the Sudan are 06.00–10.00 and 14.00–18.00 hr in winter; 05.00–08.00 and 16.00–18.00 hr in summer when day temperatures may exceed 45° C. The main types of activity are described and observations made on periodicity in other types of behaviour viz: defaecation, chewing the cud, standing, lying, drinking, feeding, playing and courtship. These are all related to ambient temperature, time of day and season of year.

Field observations at Sheerness suggest thatE. flavicaudis is night-active: it fluoresces strongly in ultra-violet light. Aktograph experiments demonstrated a marked circadian rhythm of noctural locomotory activity whose free-running period in constant light is 24.7 h. In darkness, the free-running period is variable. The rate of transpiration is not unduly low compared with that of other scorpions, as might have been expected wereE. flavicaudis day-active. It is argued that the survival of this species in southern England does not involve any special physiological adjustments since most if not all species of scorpions are able to withstand freezing temperatures.

The importance of the amphibian skin for eliminating CO2 was tested by measuring the blood pH of B. REGULARIS placed for varying periods in buffer solutions (pH 7.0 and 4.9) or swathed in latex. Blood pH did not vary from pH 7.5, except after being swathed in latex, when it dropped to pH 6.5. Respiratory movements were significantly lower when toads were submerged than when they were breathing air, and lower in water at 20°C and in the buffer solutions than in water at 30°C. It is concluded that pulmonary and cutaneous respiration are closely adjusted in this species.

During the late Pleistocene, the Sahara experienced both pluvial and inter‐pluvial periods when the climate was successively wetter and drier than it is today. At the end of the Pleistocene the regions bordering its southern edge were richly supplied with lakes and rivers. These dried up between 7000 and 3500 B.P. as the climate became progressively drier and warmer. Subsequent impoverishment of the flora and fauna has been due almost entirely to human activities: bad agriculture, felling trees for fuel, and overgrazing by domestic stock.

Water is lost by transpiration at relative humidities (R.H.) as high as 98% at 27° C and there is no evidence of the uptake of moisture through the integument from unsaturated air or moist surfaces. Water-loss through transpiration is directly related to saturation deficiency and there is no ‘critical’ transitional temperature at which the cuticle becomes porous. Nevertheless, water is retained more efficiently in Scolopendra than it is in Lithobius, suggesting an adaptation to hot-dry environments. The mean supercooling point of large specimens conditioned in an insectary is —3.1 ± 0.48° and a single supercooling can be injurious or fatal. This indicates that cold winter weather must be avoided by burrowing deeply. Aktograph experiments show that these centipedes are nocturnal. The rhythm persists in darkness at constant temperature, but is quickly lost in constant light. Resume REACTIONS A L'HUMIDITE ET A LA TEMPERATURE ET RYTHME JOURNALIER CHEZ DES MYRIAPODES SCOLOPENDROMORPHES Les Myriapodes etudies montrent une perte d'eau par evaporation lorsqu'ils sont places dans une ambiance a 27° et dont l'humidite relative est de 98%; il n'y a aucune indication permettant de penser que ces arthropodes peuvent se rehydrater a partir des surfaces mouillees ou de l'humidite atmospherique, par prelevement a travers leur tegument. La perte d'eau par transpiration est directement en rapport avec la deficience de saturation de l'air et il n'y a aucune temperature critique de transition pour laquelle la cuticule deviendrait permeable a l'eau. Neanmoins l'eau est retenue plus efficacement par Scolopendra que par Lithobius, ce qui suggere chez le premier genre une adaptation aux milieux chauds et secs. Le point de surfusion mesure pour de grands specimens maintenus en insectarium, est en moyenne de —3,1 ± 0,48° et un seul choc a cette temperature de surfusion peut etre prejudiciable ou meme fatal. Cela indique que ces arthropodes doivent eviter les froids de l'hiver en creusant plus profondement les galeries. Des experiences utilisant un actographe montrent que ces Myriapodes ont une activite nocturne. Le rythme naturel d'activite persiste a l'obscurite et a une temperature constante, mais il est rapidement perdu par exposition a un eclairement continu.

By means of choice-chamber experiments, Ocnera hispida and, to a lesser extent, Pimelia grandis were shown to exhibit photonegative responses at all temperatures while Adesmia antiqua was photopositive. The intensity of the light reactions of the first two species was not influenced by the temperature, but A. antiqua was more markedly photopositive at higher temperatures. All species respond to near-lethal temperatures by digging into the sand. Analysis of aktograph records showed that O. hispida and P. grandis are strictly nocturnal, A. antiqua diurnal in habit, The endogenous chronometer in P. grandis is retarded by cold, but is not re-set. Resume LES REPONSES A LA LUMI***ERE ET LES RHYTHMES DIURNES CHEZ LES TENEBRIONIDES DESERTICOLES. Des experiences effectuees au moyen d'une “choice-chamber” ont demontre que O. hispida et a un degre inferieur P. grandis ont des reponses photonegatives a toutes les temperatures, tandis que A. antiqua est photonegative. L'intensite des reactions a la lumieGre des deux premieGres espeGces n'a pas ete influencee par la temperature, mais A. antiqua etait nettement plus photopositive a des temperatures plus elevees. Aux temperatures subletales toutes les espeGces repondent par un enfouissement dans le sable. L'analyse des donnees aktographiques a demontre que O. hispida et P. grandis sont rigoureusement nocturnes, tandis que A. antiqua est une espeGce diurne. Le chronomeGtre endogeGne chez P. grandis est retarde par le froid, mais le retard n'est pas rattrape.

Water-loss in Paradesmus gracilis depends upon temperature and humidity, and is directly related to saturation deficiency. There is no evidence of any ‘critical point’ to indicate an epicuticular wax layer. Water is readily lost and taken up through the cuticle, the effect of the spiracles and of excretion being negligible. Despite great sensitivity to desiccation, there is nevertheless some degree of impermeability. The cuticle is in many ways similar to that of an insect: it is composed of a ‘cuticulin’ epicuticle, a ‘tanned’ chitinous exocuticle, and a laminated endocuticle of two optically distinguishable layers. The outer endocuticle is strongly calcified. The cuticle is penetrated by pore canals and the ducts of dermal glands. The latter are concerned with the production of exo- and endocuticle, and the secretion of the polyphenols which tan the protein of the exocuticle. The double hardening is probably a specialized condition of millipedes. Transpiration is almost quadrupled by extraction with hot, but not cold chloroform, as the exocuticle is impregnated with lipoids which reduce permeability. These are secreted by epidermal and dermal gland cells, and pass up the pore canals and gland ducts.

The transpiration rate of P. jannonei is lower than that of M. pruinosus, and low even compared to that of the desert woodlouse, H. reaumuri of North Africa. Different populations of the same species of woodlouse may have transpiration rates which are related to the xeric nature of their environment, but rapid acclimation in the rate of water-loss does occur. Both species, however, show quick acclimation to high and low temperature, not only as regards their time of survival in saturated air at 41·5°C (L.T. 50 for exposure of 30 minutes) but also in their metabolic rates.

Galeodes arabs is shown by aktograph experiments to be nocturnal in habit especially in the hot season. It has a low rate of water-loss by transpiration in dry air. Behaviour responses to enemies and prey are classified as alertness, threat, high intensity threat (accompanied by stridulation) leading to attack or flight (often followed by displacement sand-digging). Feeding habits are described. RESUME QUELQUES ASPECTS DE LA PHYSIOLOGIE ET DU COMPORTEMENT DE GALEODES ARABS Les moeurs nocturnes, particulierement durant la saison chaude, des araignees Galeodes arabs ont ete montrees par des experiences avec l'actographe. Dans la nature elles passent la journee dans des abris profonds, dont l'ouverture est fermee par un tampon de feuilles mortes. Leur perte en eau par transpiration a Fair sec presente un taux assez bas et elles peuvent survivre a une forte dessiccation. Leurs reactions de comportement vis-a-vis des ennemis et des proies sont classees en promptitude, frayeur, frayeur tres intense (accompagnee de stridulation) conduisant a l'attaque ou a la fuite (souvent suivie de deplacement avec rejet de sable). Les habitudes alimentaires sont decrites et on montre que la fuite se produit plus facilement chez mâles que chez les femelles.

The species of woodlouse investigated are known to stand in the following order as regards the rate of water loss by transpiration: Philoscia muscorum > Oniscus asellus > Porcellio scaber > Armadillidium vulgare. The intensity of the responses of the four species to humidity at room temperature (18±2° C.) are compared and are shown to stand in the same order. The intensity increases as desiccation proceeds. At low temperatures (3±2° C.) the intensities of the reactions to humidity are much reduced and are the same in all species; at higher temperatures (30±2° C.) the humidity responses of Ph. muscorum and O. asellus are again somewhat reduced, and it is suggested that this may be correlated with a lower thermal death-point and the need to effect a reduction in body temperature by evaporation. The antennal cone sensillae are shown to be contact chemo-receptors; no specific sense organs are concerned with the appreciation of humidity. The response is correlated with saturation deficiency rather than with relative humidity and is probably engendered by dehydration. Ph. muscorum is the most strongly photo-negative of the species and there is a graduation through O. asellus and P. scaber to A. vulgare which is the least so. Ph. muscorum is also shown to be the most intensely nocturnal in habit, A. vulgare the least. It is therefore suggested that the degree of nocturnal activity is correlated with the ability to withstand water loss by transpiration. The results obtained are discussed in relation to the ecology of the species.

Apart from artificial alteration of photoperiod to influence egg‐lay in poultry, existing knowledge of the physiology of diurnal rhythms has scarcely been applied in animal husbandry. The present a...

SUMMARY. The behaviour and sensory physiology of Paradesmus gracilis (C. L. Koch) and Blaninlus guttulatus (Bose) have been investigated. Both species posses a dermal light sense, and respond to light stimuli by means of a simple orthokinesis. Their temperature reactions fall into three categories: a general orthokinetic metabolic effect upon speed of locomotion, duration of spiral reflex, etc., a preference shown klinokinetically for temperatures about 15°C.; and orthokinetic activity stimulated by sudden drops in temperature. The temperature sense cannot be aseribed to any particular sensillae, but resides in the antennae as well as elsewhere. Positive geotaxis become apparent under the influence of the orthokinesis engendered by desiceation. The Tomosvary organs may be gravity receptors, but if so the stimulation of various proprioceptive organs by the weight of the body acting on limtes is probably also concerned in the reception of the stimulus. No orthokinetic response to humidity comparable with that found in woodlice and wireworms has been observed: the millipedes show maximum locomotory activity at all humidity ranges, but once they have finally come to rest, they do not readily start moving again. Responses to moisture, however, are far more important in their behaviour; they are purely orthokinetic, and probably a general effect of dehydration. Possibly both Tomosvary organs and trichoid sensillae register vibrations: the millipedes respond by curling up (spiral reflex), but very slight vibrations frequently stimulate locomotory activity. Reactions to contact stimuli are of very great significance in the behaviour of millipedes. They are chiefly orthokinetic, and the tactile hairs on the limbs, sides of the body, and particularly on the antennae are the sensory receptors. Millipedes do not respond to odours, but there is an orthokinetic “attraction” to gluclose and sucrose with a threshold about 0·5 gm. litre. There is no attraction to asparagine and strach, but urea repels Blavials. Antennary and gnathochilarial basiconic sensillae are the receptors for contact chemical stimulation. Removal of, or painting over the antennae induces a state of depression which persists until death. The significance of the behaviour and sensory responses of millipedes in relation to their ecology is discussed with particular reference to the importance of Blaniulus as an agricultural pest.