118 STATE OF DEVELOPMENT OP [Chap. XL 



ness that within the known history of the world or- 

 ganisation 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 inter- 

 mediate 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 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 be- 

 lieved to be " in fact more highly organised than a fish, 

 although upon another type " ? In the complex strug- 

 gle for life it is quite credible that crustaceans, 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. Besides these inherent 

 difficulties in deciding which forms are the most ad- 

 vanced 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 

 molluseoidal animals, namely, cephalopods and brachio- 



