290 STATE OF DEVELOPMENT OF [CHAP. XL 



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 organisation. 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 organised than a fish, although upon another type " ? 

 In the complex struggle for life it is quite credible that crusta- 

 ceans, not very high in their own class, might beat cephalopods, 

 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, cephalopoda 

 and brachiopods, swarmed in numbers ; at the present time both 

 groups are greatly reduced, whilst others, intermediate in organi- 

 sation, have largely increased; consequently some naturalists 

 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 the brachiopods, and 

 the fact that our existing cephalopods, though few in number, 

 are more highly organised 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 at this increase 

 in number in the highest class, which implies a great displacement 

 of lower forms, as a decided advance in the organisation of the 

 world. We thus see how hopelessly difficult it is to compare with 

 perfect fairness under such extremely complex relations, the stan- 

 dard of organisation of the imperfectly-known faunas of successive 

 periods. 



We shall appreciate this difficulty more clearly, by looking 

 to certain existing faunas and floras. From the extraordinary 

 manner in which European productions have recently spread 

 over New Zealand, and have seized on places which must have 

 been previously occupied by the indigenes, we must believe, that 

 if all the animals and plants of Great Britain were set free in 

 New Zealand, a multitude of British forms would in the course 

 of time become thoroughly naturalised there, and would exter- 



