118 STATE OF DEVELOPMENT OF [Chap. XL 



clearness that within the known history of the world 

 organisation has largely advanced. Even at the present 

 day, looking to members of the same class, naturalists 

 are not unanimous which forms ought to be ranked as 

 highest : thus, some look at the selaceans or sharks, 

 from their approach in some important points of struc- 

 ture to reptiles, as the highest 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 preponderant 

 in number ; but formerly selaceans and ganoids alone 

 existed ; and in tliis case, according to the standard of 

 highness chosen, so will it be said that fishes have 

 advanced or retrograded- in organisation. To attempt 

 to compare members of distinct types in the scale of 

 higliness seems hopeless; who will decide whether a 

 cuttle-fish be liigher than a bee — that insect which the 

 great Von Baer believed to be " in fact more highly 

 organised 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 

 oephalopods, the highest molluscs ; and such crustaceans, 

 though not highly developed, 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 deciding which forms are the 

 most advanced in organisation, 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 balance — but 

 we ought to compare all the members, high and low, at the 

 two periods. At an ancient epoch the highest and lowest 

 molluscoidal animals, namely, cephalopods and brachio 



