8 POPULAR SCIENCE MONTHLY. 



The sea-snail (Liparis), an ally of the sculpin, with scales lost and 

 fins deteriorated, is an example of a low type which is specialized as 

 well as degraded. 



In the earlier history of ichthyology, much confusion resulted from 

 the misconception of the terms 'high' and 'low.' Because sharks ap- 

 peared earlier than bony fishes, it was assumed that they should be 

 lower than any of their subsequent descendants. That the brain and 

 muscular system in sharks was more highly developed than in most 

 bony fishes seemed also certain. Therefore, it was thought that the 

 Teleost series could not have had a common origin with the series of 

 sharks. It is now understood that evolution means chiefly adaptation, 

 and adaptation among fishes is almost as often degradation as advance. 

 The bony fish is adapted to its mode of life, and to that end it is 

 specialized in fin and skeleton rather than in brain and nerves as com- 

 pared with its ancestors. All degeneration is associated with special- 

 ization. The degeneration of the blind fish is a specialization for better 

 adaptation to life in the darkness of caves; the degeneration of the 

 deep-sea fish meets the demands of the depths; the degeneration of 

 the globe fish means the sinking of one line of functions in the extension 

 of some other. 



Referring to his own work on the fossil fishes in the early forties, 

 Professor Agassiz once said to the writer : 



At that time I was on the verge of anticipating the views of Darwin, but it 

 seemed to me that the facts were contrary to the theories of evolution; we 

 had the highest fishes first. 



This statement leads us to consider what is meant by 'high' and 

 *low.' Undoubtedly the sharks are higher than the bony fishes in the 

 sense of being nearer to the higher vertebrates. In brain, muscle, teeth 

 and reproductive structures, they are also more highly developed. In 

 all skeletal and cranial characters the sharks stand distinctly lower. 

 But the essential fact, so far as evolution is concerned, is not that the 

 sharks are high or low. They are in almost all respects distinctly 

 generalized and primitive. The bony fishes are specialized in various 

 ways through adaptation to the various modes of life they lead. Much 

 of this specialization involves corresponding degeneration of organs 

 whose functions have ceased to be important. As a broad proposition, 

 it is not true that 'we had our highest fishes first,' for in a complete 

 definition of 'high' and 'low,' the specialized perch or bass stands 

 higher. But whether true or not, it does not touch the question of evo- 

 lution wliich is throughout a process of adaptation to conditions of life. 



In another essay. Dr. Coues has compared species of animals to ' ' the 

 twigs of a tree separated from the parent stem. We name and arrange 

 them arbitrarily in default of a means of reconstructing the whole tree 

 according to nature's ramifications." 



