XVI INTRODUCTION. 



the surface of the skin is divided into small rectangular spaces by trans- 

 verse folds traversed by longitudinal grooves or furrows. Limbs are absent, 

 or only prcsnit in front. Chirotes, a Mexican genus, has the fore limbs; 

 the other genera are footless. Most of the species are said to be found in 

 or about the nests of ants. One species, Lepidosternon floridanum Bd., 

 inhabits the Southeastern United States. 



Ophidia. — Serpents. 



The elongate spindle-shaped or subcylindrical form of the snake is a 

 familiar one. There are species which present no distinction between head, 

 neck, and tail, and there are others in which these parts are well marked. 

 The majority have no limbs; a few have rudimentary hind limbs, which 

 appear as claws on each side of the vent. A sternum is lacking, but in the 

 worm-snakes there are rudiments of a pelvic arch. Most of the serpents 

 have teeth on jaws and palate. In consequence of the elastic articulations 

 of the bones of the skull and the symphysis of the lower jaws, they are 

 able to swallow animals considerably larger than would otherwise be possi- 

 ble. All the species of the order are carnivorous. Some crush their prey 

 in the folds of the body, others kill the creatures on which they feed by 

 venomous secretions, but the greater number swallow living food. During 

 the operation of swallowing, small pores along the jaws give out a saliva 

 which renders the act more easy. Frequently the snake disgorges a partly- 

 swallowed meal to change its position in the mouth, or to take breath; the 

 slimy appearance of such morsels has given rise to the erroneous idea that 

 they have been deliberately covered with slime before the attempt to dine. 

 Movable eyelids do not exist in the Ophidia. The epiderm is continuous 

 over body and head, and forms a transparent cover for the eyeball. With 

 the slough or cast skin the outer envelope of the eye is carried away; this 

 happens at least once in a season. 



Near the time of sloughing or moulting, the dermal covering of the eye is 

 loosened, more opaque, and interferes, to some extent, with the sight ; at such 

 times snakes are said to be blind. Size of ball, shape of pupil, keenness 

 of sight, etc., vary according to the habits of the species. Hearing is dull. 

 There are no external evidences of ears, and it is most likely the jar felt over 

 the whole body from an approaching tread often gives the needful warning. 

 The hissing sound produced by expelling the breath from the lungs has been 

 supposed to be the nearest approach to a voice. Lately, however, some 



