LESSONS IN ZOOLOGY. 299 



branchial respiration, and every form of metamorphosis Rep- 

 tiles generally are tenacious of life ; can to some extent replace 

 lost parts ; can live- for long periods without food, and with but 

 limited respiration. 



The Ophidm, or snakes, have elongated cylindrical bodies, 

 usually without limbs ; sometimes limbs are represented by small 

 spurs on the sides of the vent. They have an epidermal cover- 

 ing of scales, which are usually somewhat elongated, and may 

 be smooth or provided with a longitudinal ridge. The head is 

 covered with irregular-shaped plates, the abdomen with broad 

 band-like plates, while the subcaudal plates are in pairs. The 

 anal plate is sometimes entire and sometimes bifid. The number 

 of rows of scales, the number of ventral plates and the charac- 

 ter of the anal plates and body scales are important specific char- 

 acteristics. The ribs, of which they have great numbers, are the 

 chief locomotive organs of snakes. The free ends of the ribs are 

 attached to the abdominal plates by muscular fibers, so that the 

 ribs serve as legs and the plates as claws. The skin is shed and 

 replaced at somewhat regular intervals ; they have a forked pro- 

 trusible tongue and no eyelids. 



The Colubrifonma, have both jaws armed with solid hooked 

 teeth, with no poison fangs, and no spur-like appendages near 

 the vent. This group includes the spreading vipers, watersnakes, 

 garter snakes, blacksnakes, the racers, milk snakes, and other 

 common snakes of our country. The harlequin, or bead snake, 

 which is much like the members of this group in general appear- 

 ance, has two grooved poison fangs in the upper jaw. It is jet 

 black, with seventeen broad crimson rings, spotted with black, 

 while the tail has yellow rings. 



The Crotalidse have the upper jaw provided with an erectile 

 grooved poison fang on each of the relatively small upper jaws, 

 and the short tail is often provided with a rattle. This group 

 includes the rattlesnakes, massasaugas, .copperheads and moc- 

 casins. 



The Lacertilia or Lizards, are sometimes snake-like in form, 

 but as a rule they have two pairs of limbs, and the body is usually 



