14 Hans Gadow, 



Consequently tlie causes of these clianges and their orthogenesis 

 must be both environmental and constitutional ; and tlie cases of isotely, 

 eventually of mimicry, are the effect of the same environmental 

 agencies lipon a similar organic substratum. Tliere is a cause for 

 the increased production of melanine, and another for red pigment; 

 say, deficiency of certain light wliicti disfavours black and enhances 

 red, and if this condition continues, erytlirism will in the long run 

 assert itself, and ultimately there will be descendants born red 

 without a trace of black. And where the first patch of red shall 

 appear first, is a constitutional question, just as is the peculiar 

 mode of growth of an ocellus; and the deposition of mineral salts 

 is also constitutional, The same applies to the concentration of black 

 into rings. Although possibly influenced by the affinity of the respective 

 pigment the cells will congregate and increase where the surrounding 

 tissues makes it easiest for them. Further, in such eminently bilateral 

 creatures as snakes, symmetry is a powerful factor, and since they 

 are also very elongated, repetition asserts itself. It is not accidental 

 that on depressed bodies longitudinal striation gives way to trans- 

 verse pattern, and that this itself is easiest to accomplish on narrow 

 and long bodies, witness the tail. Of course there are many lizards 

 and snakes with striped tails, but then their bodies are also striped 

 in the same way ; but a survey of longtailed creatures shows the 

 frequency of a banded tail whilst the body is still striped, or still 

 ocellated, or still patchy. The Jaguar's body and tail are marked 

 by the same principle of rosettes, but whilst these remain separate 

 on the hodj they are fused into confluent rings on the tail. The 

 vertebrate tail is not a mere appendage, it has in many respects a 

 longer history than the body. 



Concerning the pattern of the tail of our elapoid-coloured snakes, 

 it is safe to State that in the overvvhelming majority the tail is 

 sharply and completely ringed, and bicoloured, black and yellow or 

 black and wiiite, wiiilst the hodj is still in the tricoloured phase 

 and in process of Variation, the drift of which is obvious. Perhaps 

 these conditions may underlie Eimee's law of hystero-protero undu- 

 lation, a principle by no means universal, but at least suggestively 

 frequent. 



Although all the elapoid-coloured snakes show an unmistakable 

 drift towards either melanism or erythrism, we have no right to 

 expect that they will all end in either black or red species. Being 

 so plastic, in such a Üux, and so easily reacting upon external 



