NATURAL SCIENCES OF PHILADELPHIA. 



289 



Pairs of black rings ; 



Opheomorphus mimus. d 



Erythrolamprus venustis- 



simus. a 

 Ophibolus polyzonus. a 

 Xenodon bicinctus. b 



Single black rings, far apart 

 Elaps corrallinus. b 



nigrocinctus. c 

 Pliocerciis equalis.c 



Oxyrrhopus ? 



Erythrolamprus albosto- 

 latus. b 



Single black rings, very close 

 Elaps mipartitus. d 



Pliocercus euryzonus. d 



Oxyrhopus petolarius. d 

 Scolecophis zonatus. a 



Leptognathus anthra- 

 cops. a 



Species a, from Mexico and Central America. 

 " b, " Brazil, Venezuela. 

 " c, " Central America. 

 " d, " -western side of Andes. 

 " h, " Arizona and Sonora. 



Many of the species in the same column are exceedingly similar, and some 

 ^ have^ittle (perhaps nothing) to distinguish them but generic characters. The 

 most similar are almost always from the same sub-region. 



Similar analogies have been pointed out by Bates among the Lepidoptera 

 of Brazil, and by Wallace among those of Borneo and Celebes, etc. I call 

 attention to these authors, here without copying them, as they will repay pe- 

 rusal in the originals. 



A case of analogy which may belong to this class is that of the three genera 

 Chelys among tortoises, Pipa among frogs, and Aspredo among Siluroid 

 fishes, species of which inhabit at the same time the rivers of Guiana. The 

 crania of these genera are similarly excessively flattened and furnished with 

 dermal appendages, and their eyes are very minute. The singular similarity 

 need only be mentioned to those familiar with these genera, to be recognized. 



The bearing of the Mimetic analogy on the question of transition of types 

 in the developmental hypothesis, is its demonstration of the independence of 

 generic and specific characters of each other, which may suggest the possibility 

 of the former being modified without affecting the latter. 



These facts might have been introduced under Sect. list, but they illustrate 

 the general laws of the present section. 



IV. Of natural selection. 



rt. As affecting ordinal and class characters. 



The second law which may be supposed to have governed a descent with 

 modification, in the production of existing genera, is the force which the will 

 of the animal applies to its body, in the search for means of subsistence and 

 protection from injuries, gradually producing those features which are evi- 



1868.] 



