OPIILDIA. 233 



single piece with the rest of the epidermis. No Snakes have an 

 ear-opening. The tongue is smooth, bifid, and retractile into a 

 basal sheath. Limbs are absent, and the animal moves by lateral 

 undulations. 



The primary division of Ophidians into poisonous and non- 

 poisonous must be regarded as unscientific ; and, although adopted 

 almost generally, it is in so far incorrect that a number of forms 

 (OpisilioylypluC) usually ranked as harmless are really poisonous, 

 although their bite may be without effect on man and large animals. 

 Experiments recently made on Qodopettis, a genus allied to Psammo- 

 phis *, and Dryopku t, have shown that these snakes are poisonous, 

 and that, they paralyze their small prey before deglutition. It is 

 probable that all Snakes with grooved teeth will prove to be 

 poisonous, to a greater or less degree, as it is clear, a priori, that 

 these grooved fangs are not without a function. I have therefore 

 abandoned this physiological character in dividing the Snakes into 

 families. Poisonous as well as harmless forms are arranged under 

 Colubridie. All Viperidce are poisonous. 



The poison-gland is situated on each side above the upper jaw, 

 below and behind the eye, and in some Elapoid forms even extends 

 far back along each side of the body. This gland communicates 

 by a duct with the poison-fangs, which are enlarged, channelled or 

 " perforated " teeth. The difference between channelled and per- 

 forated fangs is but one of degree, and the term " perforated " is 

 anatomically incorrect. In both these types, the structure of the 

 teeth is essentially the same ; they are folded over so as to form a 

 duct to carry the poisonous secretion ; when the edges meet and 

 coalesce, a perforated fang is formed, when they merely approach 

 each other, the channelled form results. 



A general desire is felt by those not well acquainted with Snakes 

 to be able to distinguish at a glance between harmless and 

 poisonous forms. To meet this requirement, various criteria have 

 been proposed by authors, none of which, however, are satisfactory. 

 It is well to state at once that there is no sure method of dis- 

 tinguishing the two kinds by external characters ; except, of course, 

 by a knowledge of the various forms. And even then, a cursory 

 examination is not always sufficient, since there is, in some cases, a 

 striking resemblance between Snakes of totally different affinities, 

 by which even specialists may be at first deceived. In short, 

 nothing but an examination of the dentition can afford positive 

 information as to the poisonous or non-poisonous nature of an 

 unknown Snake. 



About 1500 species of Snakes are known. They may be arranged 

 in nine families, all represented in India, and defined in the fol- 

 lowing synopsis. 



* Peracca & Deregibus, Arch. Ital. Biol. v, 1884, p. 108. 

 t Vaillant, Mem. Cent. Soc. Philom. 1888, p. 44. 



