0^ THE OEIGm OF GENERA. 57 



yiduals of the same species of any of tliese genera, to render a 

 hypothesis of evolution a demonstrated fact.* 



It must be here observed that great size indicates little or 

 nothing as to zoological rank. The greatest species are often not 

 far removed in affinity from the least ; thus there can be but little 

 doubt that elephants are not far removed from the rodents, and 

 the rhinoceros is near the cony. Indeed, in the same genus the 

 most extraordinary diversity prevails, for we have a very small 

 elephant of Malta, and in the Miocene of Maryland a fin-back 

 whale not so large as the new-born young of the fin-backs now 

 living. Hence the . objection to the developmental hypothesis, 

 based on the great size of the primal Selachians and Ganoids, has 

 but little weight. 



7. Eathke has shown that the arteria ophthalmica of the 

 higher Ophidians is originally a branch of the arteria cerebralis 

 anterior, and that it later forms a connection with the arteria 

 facialis. This connection increases in strength, while the other 

 diminishes, until finally its supply of blood is derived from the 

 facialis instead of the cerebralis. 



Eathke has also shown that the cerebral origin of this artery 

 is continued through life in the three lowest suborders of the ser- 

 pents, the Scolecophidia, Catodonta, and Tortricina ; also in the 

 next succeeding group, the Peropoda. 



8. In most serpents the left lung is never developed ; in such 

 the pulmonary artery, instead of being totally wanting, remains 

 as a posterior aorta bow, connected with the aorta by a ductus bo- 

 talli ; serpents without left lung being therefore identical in this 

 respect with the embryonic type of those in which that lung 

 exists. 



9. Dr. Lespes states that the optic region of the brain of blind 

 cave Coleoptera, examined by him is similar in structure to that 

 in the blind larvae of Coleoptera, whose images possess visual 

 organs. 



10. t Those Saurians (Uromastix, etc.), in which the pre- 

 maxillary region is produced into a uniform cutting edge, are 

 furnished during early stages with a series of premaxillary teeth, 

 which become gradually fused and confluent with the alveolar 

 margin. Hence other Acrodonts are equivalent, in this respect, 



* This variability has since been shown to exist in species of the M. angmlidens 

 type (1886). 



f See under section on Acceleration and Retardation. 



