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 Eimer’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 in 
the embryo which mark the course of subcutaneous 
blood-vessels. Zenneck found that in the adult the 
