1905.] NATURAL SCIENCES OF PHILADELPHIA. 207 



An examination of the evidence for utility in generic and specific 

 characters in serpents was undertaken, chiefly for the reason that the 

 relative simplicity of their organization and the nature of the charac- 

 ters which meet with general acceptance as of taxonomic value seemed 

 likely to afford exceptions to Mr. Wallace's law. The result appears to 

 be that if the validity of specific characters depends solely upon utility, 

 species are few, many genera now including a number of accepted 

 species which Mr. Wallace would be logically bound to reduce to one. 

 Profound structural differences below family rank are not known among 

 snakes. Generic determination is made upon associations of charac- 

 ters, such as the presence or absence of hypapophyses on the posterior 

 trunk vertebrae with endlessly varying details in the form, number and 

 serial proportion of teeth, the arrangement or absence of certain head 

 plates, and differences in the scutellation upon the body. Utility is 

 evident in the presence of ventral hypapophyses, for they supply at- 

 tachment for bundles of muscular fibres running to the diapophyses 

 of several succeeding vertebra, which play an important part in throw- 

 ing the body into curves. They are found in most aquatic species 

 except in Hydroyhince, where they are largely developed upon the tail. 

 But they are present in groups as widely separated otherwise as the 

 so-called Natricince among colubrine snakes, the Elapinoe among pro- 

 teroglyphs, and in Viperidoe. They are, therefore, of no value, taken 

 separately, as measures of affinity. The elapine and viperine snakes 

 are not usually aquatic, and in them utility has doubtless had relation 

 to the rapidity and force required in striking and the need of firm sup- 

 port for the hinder part of the body during the act. In fact, the distri- 

 bution of these structures seems to afford a true case of convergent 

 evolution. 



While utility was primarily concerned in the development of teeth 

 generally, it does not follow that the endless trifling differences in 

 the teeth of Colubridce and Boidce are due to the same cause, 

 for they do not present distinctive types, as in mammals and many 

 lizards, having a mechanical relation to kind of food, but seem, on the 

 whole, to be promiscuously distributed. That such minute differences 

 are due to internal laws of growth and are reached by Natural Selection 

 only when they become hurtful, is much more intelligible than that 

 utility has required such endless variety of minute adaptations. It is 

 admitted that by referring a structure to "laws of growth" no more is 

 accomplished than to express a belief in the action of organic causes 

 whose exact nature is not yet known. 



In head plates the differences commonly met with are in the absence 

 or fusion of certain ones upon the snout. That the presence or ab- 

 sence of a minute fissure between any of these plates, which are under- 

 laid by the bony skull and incapable of flexure, can have selective value 

 is inconceivable, and the frequency of their occurrence in degraded, 

 burrowing species points clearly to the probability that they result 

 from the direct action of external stimuli and are of too little import- 

 ance to be acted upon by Natural Selection. In fact, the almost 

 invariable occurrence of these anomalies in burrowing species is a 



