Colouration of Vertebrata. 89 



marked by a dark line. These facts point distinctly to structural 

 decoration. 



There are in some fishes, like the John Dory, curious eye-like 

 dark spots, which we cannot refer to a structural origin, though a 

 better acquaintance with the class might reveal such significance. 



The Amphibia have not been well studied by us, and we must 

 leave them with the remark that they seem to bear out the view of 

 structural decoration, as is seen in our English newts. Some are, 

 however, modified out of all easy recognition. 



Reptiles. Among the reptiles, the snakes, Fig. 4, may be selected 

 for illustration. Snakes are practically little more than elongated 

 backbones, and are peculiar from the absence of limbs. The colour- 

 ing matter does not reside so much in the scales as in the skin 

 beneath, so that the sloughs do not illustrate the decoration. 

 Hence, we might expect to find here a direct effect of morphological 

 emphasis. 



The ornamentation of snakes is very similar throughout the class, 

 both in water and land snakes ; as may be seen by Sir W. Fayrer's 

 work on Venomous Snakes. This ornamentation is of a vertebral 

 pattern, placed along the dorsal surface, with cross lines, which may 

 represent ribs. 



Where the ribs are wanting, as in the neck, the pattern changes, 

 and we get merely longitudinal markings. 



In the Python, Fig. 4, there are, near the central line, numerous 

 round spots, which apparently emphasize the neural processes. 

 There are diagonal markings on some species which illustrate the 

 development of colour-spots already alluded to. 



This snake-pattern is very singular and striking. The markings 

 are fewer in number than the vertebras, yet their true vertebral 

 character is most obvious. 



In Snakes, again, we find the dorsal region is darker than the 

 ventral. 



In the Lizards there are patches of colour placed axially, while 

 each patch covers a number of scales. 



Birds. Birds have their whole economy modified to subserve 

 their great functional peculiarity of flight. 



Immense muscles are required for the downward stroke of the 

 wing, and to give attachment to these the sterum has a strongly 

 developed keel. To bring the centre of gravity low, even the 

 muscles which raise the wing are attached to the sternum, or breast- 



