show the same colour. This empirical choice certainly has its reasons which we 

 are at present unable to recognise. It should also be pointed out that for all diurnal 

 terrestrial animals of the desert the strong radiation from the soil is an important 

 ecological factor. Their black colour may be the consequence of raised melanin pro- 

 duction as a reaction to certain parts of the solar spectrum, just as melanin is in- 

 creased by higher metabolic activity. The latter has been experimentally demon- 

 strated in the phases of the Desert Locust (Schistocerca gregaria), where the black 

 colour of the gregarious hoppers contrasts with the pale green of the hoppers of the 

 solitary phase. Superimposed on the effect of raised activity is the effect of the 

 hours of sun basking (i.e. of intensive exposure to solar radiation) which are greatly 

 prolonged, especially in the first stages of the gregarious hoppers as compared with 

 the solitary ones. Another mechanism produces adaptive black colouration among 

 the animals found in areas of black lava, (e.g. Agama stelliopicae), or on burnt or 

 otherwise blackish soil (as in many grasshoppers). 



Of special interest is an internal black pigmentation in the peritoneum and 

 pleura of desert reptiles. Alpine climatologists stated some decades ago that alpine 

 lizards (Lacerta spp.) show black pigmentation of this kind. We have just begun to 

 pay attention to this phenomenon in our region, and we find it to be of common oc- 

 currence in lizards with diurnal summer activity, such as Acanthodactylus, Lacerta, 

 Agama, Eremias, etc. The deepest, velvet -black pigmentation of this type occurs 

 in the chameleon, which is especially exposed to sun radiation. In some species, 

 even the omentum and its fat show patches of black pigment. Before speculating 

 about these phenomena we must have information as to whether black pigmentation 

 is common to lizards and snakes in more northern climates. Some English species, 

 Lacerta vivipara and L. agilis possess a black peritoneum, whilst Anguis fragilis, 

 Vipera berus and Matrix natrix do not. The long exposure to strong solar radiation 

 of all diurnal desert animals between spring and autumn raises a number of questions 

 of physical physiology. The first and most important of these is to what degree the 

 rays of various wave- length in the solar spectrum are able to pierce the dead part 

 of the integument. We therefore undertook (in co- operation with Drs Halperin and 

 Svirski) some preliminary measurements on the transmission of rays through the in- 

 tegument of freshly killed insects and reptiles. The experiments were conducted 

 with a Beckman Quartz spectrophotometer. The results indicated that the actual 

 quantity of transmission depends primarily upon the intensity of the radiation. 

 Through the transparent wings of a dragonfly (Crocothemis) transmission in all ran- 

 ges of the spectrum is very high, even higher than for normal glass. Yet through all 

 other objects transmission in the ultra-violet range is nil, except perhaps for a slight 

 transmission through the white -scaled forewings of Pieris rapae.. Some slight trans- 

 mission is always observed in the higher range of the visible spectrum, whilst trans- 

 mission is always important in the infra-red range, where in all cases it reached a 

 maximum at 1200fi. This applied also to black insects. In the reptiles we had ex- 

 pected some ultra-violet transmission as we had regarded the black pigmentation of 

 the integument as a reaction against it. Instead, transmission of ultra-violet through 

 the skin of back and belly of Ophisops elegans and two other lizards {Chalcides 

 and Eumenes) was found to be absolutely nil. It was very low in the visible part of 



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