CROCODILIANS, LIZARDS, AND SNAKES. 715 



or to produce some eggs ;iud some living young at the same time.' There are, 

 indeed, oviparous snakes and snakes which are ovoviviparous, and there is a 

 conspicuous difl'erence in their eggs. The eggs of the oviparous species are fur- 

 nished with a thick, tough, flexible covering or "shell," while the eggs of the 

 species which produce living young have coverings which are very thin and 

 delicate. Now, should such eggs as the latter be laid any considerable period 

 before the young are ready to be excluded, the thin envelopes would surely be torn 

 during the writhings of the embryo. That some of the eggs may be partially 

 developed at the time when the embryos of other eggs are ready to be ushered 

 into the world, and that all may be expelled together, is possible; but this is not 

 the normal course of things and may not be well for the immature young. Normally 

 the coverings of such eggs are ruptured before birth or immediately afterwards. 

 On the other hand, it is quite probable that the eggs of the oviparous species are 

 laid a considerable period before they are hatched. The tough coverings of such 

 eggs protect them from attacks and injuries from without and at the same time 

 resist the movements of the young snake within. So far as we know these eggs are 

 deposited in the earth in piles of decaying vegetable matter and similar places. 



A very curious structure deserves mention here. This is the " egg-tooth," a small 

 tooth fixed to the united premaxillary bones and projecting forward slightly beyond 

 the edge of the upper lip. It is present only in the embryo and is abed shortly after 

 the escape of the young snake from the egg. In the ovoviviparous species, the tooth 

 may apparently be shed before the young are born. The tooth is employed by the 

 little snake in ripping open the tough egg covering in its efforts to escape from its 

 prison. It would appear to be of little service to the young, which are mature when 

 born, since the egg coverings are so very tender; nevertheless I have found the 

 tooth present in all of the ovoviparous species whose young I have had opportunity 

 to study. This tooth, as found in the black racer, was described as long ago as 1857 

 by Dr. Weinland,- but Miiller had observed it even earlier. 



The habits of particular species of snakes are referred to uikUt the 

 respective heads. 



EPANODONTA. 



TYPHLOPIDJE. 



I. Muzzle covered above by rostral and internasal scuta. 



a. Two ocular plates and a preocular. 



One nasal plate Lcthcobia Cope. 



aa. One ocular and .a prcocular. 



One nasal plate 'I)/phlops Schneider. 



Two nasal plates Ilehniiilhophix' Peters. 



aaa. One ocular and no preocular. 



One nasal plate I'uphHtia ' Wagler. 



Two nasal plates Linli/ph lops • Peters. 



II. Muzzle and front with five symmetrical scuta. 



Two nasals and a preocular Anomahpia .Jan. 



No species of the Typhloi)idie has been found in the Nearctic realm. 

 They occur in all tropical regions. 



' Proc. Acad. Nat. Sci. Phila., 18«7, p. 121. 



-' Proc. Essex Inst., II, 185(1, p. 28, pi. i. 



■' Idioi!iphlopi< Jan. 



* niidion Dumeril and Bibron. J'upliUnaliii Gray. 



'' Rhinoiyplops Peters. 



