Changing Colour in Reptiles. 399 



can each undergo a change of hue independently of the other. 

 Taking ihe body as a whole, the number of different colora- 

 tions which Chamceleon, in particular, is able to assume 

 becomes in this way very large. Moreover, at least in Iguana, 

 Calotes, and Chamceleon vulgaris (not in all varieties), the. 

 spots may entirely disappear, which is never the case in the 

 species of the first group. It is, however, important to draw 

 attention to the fact that, so far as my experience extends, no 

 reptile that changes colour possesses the faculty of allowing 

 alterations to take place in the outlines of the spots. Since 

 the changes of tint recur with a certain regularity, it is after 

 continued observation very easy to determine that ground- 

 colour and spots always show precisely the same limitations so 

 long as the animals do not appear of one colour. If we have 

 once determined these limitations we shall find that no other 

 pattern is ever produced under all gradations of tint ; the 

 spots always occur in precisely the same part of the body and 

 have the same size and outline. Besides the faculty of 

 changing its ground-colour and the colour of its spots inde- 

 pendently of each other, Chamceleon also possesses the power 

 of producing another kind of marking. This marking con- 

 sists in the entire body of the animal appearing as if strewn 

 with numerous roundish black specks. The broad circle of the 

 eyelid is then seen to be coloured in radii. This coloration 

 only occurs when the animal is alarmed, and here also the 

 number and arrangement of the spots are, as I have convinced 

 myself, always the same. 



It would lead us too far to give an enumeration of all 

 possible changes of colour in the different species. Observa- 

 tion shows, however, that they recur with a certain regularity, 

 and consequently must also have a definite object. 



So far as it is possible to recognize this object, several 

 divisions can again be set up, according to which the power 

 of changing colour can be classified. 



In the sense of the Darwinian theory, the power of changing 

 colour may have arisen, or, let us say, have been developed : — 

 I. For the purpose of protection against enemies. 



II. As a means of absorbing or warding off heat. 



III. Through sexual selection. 



While in the case of some of the reptiles which change 

 colour only one of the objects named is to be recognized, in 

 others the change of hue fulfils two or even all of the purposes 

 referred to. 



It is to be regarded as protective coloration when Agamaj 

 and Geckos assume the tint of the ground or bark so 

 precisely as scarcely to be distinguished from the surface on 



