16 REPTILE GALLERY. 



are nearly helpless. The tongue is exceedingly long, worm-like, 

 with a club-shaped viscous end ; they shoot it out with incredible 

 rapidity towards insects, which remain attached to it, and are thus 

 caught. The eyes are almost entirely covered by a thick lid, pierced 

 with a small central hole, and not only can be moved in any direc- 

 tion, but each has an action independent of the other — one eye 

 may be looking forwards, whilst an object behind the animal is 

 examined with the other. The faculty of changing colour, which 

 they have in common with many other Lizards, is partly dependent 

 on the degree in which the lungs are filled with air, and different 

 layers of chromatophores* are pressed towards the outer surface of 

 the skin. The adult males of some of the species possess long 

 horns or other excrescences on the head. The largest species 

 attain a length of 18 and 20 inches. 



Order IV. OPHIDIA, or Snakes. 



The Snakes, or Ophidians, are scaly Reptiles, with exceedingly 

 [Cases elongate, limbless body, without sternum, without, or with only 

 rudiments of, a pelvis, with the mandibles united in front by an 

 elastic ligament. The ribs are articulated movably with the verte- 

 bral column. The jaws are armed with sharp, fang-like teeth, 

 which are ankylosed to the bone. The peculiar mobility of the 

 jaw-bones enables these animals to extend the gape in an extra- 

 ordinary degree, and to work their prey (which generally is much 

 thicker than the Snake itself and always swallowed whole) through 

 the throat into the stomach. The tongue is narrow, retractile into 

 a basal sheath, and terminates in two long thread-like points; 

 it is frequently and rapidly exserted when the animal is excited or 

 wants to touch an object. Snakes have no eyelids ; but the part 

 of the epidermis which covers the eye is transparent, convex, and 

 has the shape of a watch-glass, behind which the eye moves. There 

 is no ear-opening. The scales are not isolated formations, as in 

 fishes, but merely folds of the outer skin, which is cast off in a 

 single piece several times every year. The head is generally covered 

 with large, symmetrical, juxtaposed plates (see figs. 15 & 10), and the 



• Cells in the skin in which the colouring-pigment is deposited. 



