ANCIENT AND LIVING FOBMS. 365 



which forms ought to be ranked as highest: thus, some 

 look at the selaceans or sharks, from their approach in 

 some important points of structure to reptiles, as the high- 

 est fish; others look at the teleosteans as "the highest. The 

 ganoids stand intermediate between the selaceans and 

 teleosteans; the latter at the present day are largely pre- 

 ponderant in number; but formerly selaceans and ganoids 

 alone existed; and in this case, according to the standard 

 of highness chosen, so will it be said that fishes have 

 advanced or retrograded in organization. To attempt to 

 compare members of distinct types in the scale of highness 

 seems hopeless; who will decide whether a cuttle-fish be 

 higher than a bee — that insect which the great Von Baer 

 believed to be " in fact more highly organized than a fish, 

 although upon another type?" In the complex struggle 

 for life it is quite credible that crustaceans, not very high 

 in their own class, might beat cephalopods, the highest 

 moUucs; and such crustaceans, though not highly devel- 

 oped, would stand very high in the scale of invertebrate 

 animals, if judged by the most decisive of all trials — the 

 law of battle. Beside these inherent difficulties in decid- 

 ing which forms are the most advanced in organization, 

 we ought not solely to compare the highest members of a 

 class at any two periods — though undoubtedly this is one 

 and perhaps the most important element in striking a bal- 

 ance — but we ought to compare all the members, high and 

 low, at two periods. At an ancient epoch the highest and low- 

 est molluscoidal animals, namely, cephalopods and brachio- 

 pods, swarmed in numbers; at the present time both groups 

 are greatly reduced, while others, intermediate in organi- 

 zation, have largely increased ; consequently some natu- 

 ralists maintain that molluscs were formerly more highly 

 developed than at present; but a stronger case can be made 

 out on the opposite side, by considering the vast reduction 

 of brachiopods, and the fact that our existing cephalopods, 

 though few in number, are more highly organized than 

 their ancient representatives. We ought also to compare 

 the relative proportional numbers, at any two periods, of 

 the high and low classes throughout the world: if, for 

 instance, at the present day fifty thousand kinds of verte- 

 brate animals exist, and if we knew that at some former 

 period only ten thousand kinds existed, we ought to look 



