DISTEIBUTIOX. 325 



development of the vertebrae whicli characterizes some of 

 the more modern iishes and reptiles, when compared with an- 

 cient fishes and reptiles of the same orders ; and the '' regu- 

 larity and evenness of the dentition of the Anoj)lothe7num 

 as contrasting with that of existing Artiodactyles." 



The facts thus summed up, do not show that higher forms 

 have not arisen on the Earth in the course of geologic time, 

 any more than the facts commctily cited prove that higher 

 forms have arisen ; nor are tliey regarded by Prof. Huxley 

 as showing this. AYere the types which have survived from 

 palaeozoic and mesozoic periods down to our own daj^, the 

 only types ; and did the modifications, rarely of more than 

 generic value, which thesa types have undergone, give no 

 better evidences of increased complexity than are actually 

 given by them ; then it would be inferable that there has 

 been no appreciable advance among organic forms. But 

 there now exist, and have existed during the more recent 

 geologic epochs, various types which are not known to have 

 existed in earlier epochs — some of them widely milike 

 these persistent types, and some of them nearly allied to 

 these persistent types. As yet, we know nothing respecting 

 the origins of tliese new types. But it is quite possible that 

 causes like those which have produced generic differences in 

 the persistent types, may, in some or many cases, have pro- 

 duced modifications great enough to constitute ordinal differ- 

 ences — may have resulted in the formation of tj^es that are 

 now classed as separate. If structural contrasts not exceed- 

 ing certain moderate limits, are held to mark only generic 

 distinctions ; and if organisms displaying larger structural 

 fjontrasts are considered ordinally or typically distinct ; it is 

 clear that the persistence of a given type through n long 

 geologic period without apparently undergoing deviations of 

 more than generic value, by no means disproves the occuiTence 

 of far greater deviations ; since the forms resulting from such 

 far greater deviations, being regarded as typically distinct 

 forms, will not be taken as evidence of great change in the 



