202 DR. N. ANNANDALE ON THE FAUNA OF A DESERT TRACT IN S. INDIA. 



The question at once arises, "How does the sandy coloration of desert animals, 

 which is so well known in most sandy tracts, come about?" These Ramanad forms, occur- 

 ring in a small and probably very recent desert not separated by any great natural barrier 

 from fertile districts, are of considerable interest as regards this question. The first 

 point that becomes evident on a critical examination of them is that their pale (or paler than 

 ordinary) coloration is not essentially protective in all cases. Sitana ponticeriana, Calotes 

 gigas, and the typical form of the Indian Cobra, are undoubtedly concealed by their 

 coloration in such localities ; but the yellow Cobra of the dense Malayan forests, to which 

 I have referred above, is much more sandy than any of these, while the Ramanad 

 Typhlopidse and the Rat Snake from the same locality, though possibly rather less 

 conspicuous than if they were darker, are by no means identical with sand in colour, but 

 only have a vague approximation to it. This is especially true in the case of the T. lim- 

 brickii and the local variety of Typhlops bramtnus, which are distinctly flesh-coloured in life, 

 and of T. psammophilus, which, judging from the intense pigmentation of its eyes, may 

 be endowed with some powers of vision and therefore may exist under conditions which 

 would expose it more directly to the effects of light. It is curious that the snakes most 

 highly modified as regards colour in this locality are those which would seem to be the 

 least often exposed directly to light, as burrowers. It is well known, however, that the 

 hair of many tropical mammals, which live more or less in the shade, takes on a reddish 

 or yellowish tinge owing to exposure. I may instance the black-backed variety of the 

 squirrel Ratufa bicolor, the back of which, in specimens which have not recently cast 

 their coat, becomes distinctly reddish. We know, moreover, that, even in temperate 

 localities, some slight change may substitute yellow pigment for black in the feathers 

 of birds — a phenomena which occurs not infrequently in the Puffin {Fratercula arcticd) of 

 Iceland, where individuals with the back mottled with white and yellow, instead of being 

 black, are sometimes produced. It would, therefore, appear possible that even indirect 

 exposure to the steady glare of light that occurs in tropical and subtropical deserts may pro- 

 duce an extreme degree of yellowing in delicate organisms. The transmission of the paler 

 type of coloration thus brought about would not necessarily postulate the transmission of 

 acquired characters ; for the light might well effect the embryo in the egg or in the body of the 

 mother, the decrease in intensity of pigmentation of the adult giving, in the latter case, a 

 readier access for the light to the foetus. Indeed, it is possible that the light might even 

 affect the generative organs of the parents to such an extent that they produced, under 

 all conditions, paler offspring, which were not able to transmit to the third genera- 

 tion the power of producing pigment of great intensity. Such considerations must be 

 largely speculative, until we are in a position to state definitely not only what changes 

 are produced in the coloration of tropical animals, directly or indirectly, by environment, 

 but also what is the structural difference between different animal pigments. 



The Reptiles of Ramanad are, for the most part, forms which are sufficiently gener- 

 alized in coloration, as in structure, to survive in a considerable variety of environments, 

 without dying out individually, or perishing as species by evolution in some new 

 direction ; but a few of them exhibit very obvious modifications, probably due directly to 

 the effect of change of environment upon the breed, possibly even upon the individual. 



