XI THE COLOURS OF REPTILES 237 



to the varying susceptibilities of the chromatophores 

 to the action of light. For an elaborate discussion of 

 the coloration of the wall -lizard {Lacerta muralis) 

 the reader may be referred to Elmer's well-known 

 papers. 



The colours of snakes are often dull, and due in 

 large part to obscure mottlings, but in some cases, 

 as in the deadly coral snake {Elaps), there is a con- 

 spicuous black and red banding. As compared with 

 lizards, snakes seem to be characterised by an in- 

 creasing predominance of epidermic pigments which 

 are got rid of and renewed when the slough is cast. 

 Many would regard this again as a proof that the 

 pigments are waste products, in process of being 

 eliminated by means of the skin. The skin of 

 snakes, like that of most reptiles, contains guanin, 

 which is said by Leydig to give rise in some cases 

 to white and yellowish patches. 



Origin of Markings in Snakes 



In discussing the coloration of leeches we have 

 seen that an attempt has been made to explain this 

 on mechanical grounds, by associating the stripes or 

 spots with the development and arrangement of the 

 muscles — it is interesting to note that in snakes the 

 coloration seems to bear a similar relation to the 

 arrangement of the blood-vessels. Herr Jonathan 

 Zenneck finds that in the case of the ringed snake 

 {Trophidonotus natrix) the three longitudinal rows of 

 spots in the adult correspond to three red lines iri 

 the embryo which mark the course of subcutaneous 

 blood-vessels. Zenneck found that in the adult the 



