38o 



Classification of Fishes 



is still incomplete, and the characters are not specific, but only 

 varietal, in the literal sense of these terms." 



Generalization and Specialization.— A few terms in common 

 use may receive a moment's discussion. A type or group is said 

 to be speciahzed when it has a relatively large number of pecu- 

 liarities or when some one pecuHarity is carried to an extreme. 

 A sculpin is a specialized fish having many unusual phases of 

 development, as is also a swordfish, which has a highly pecuHar 

 structure in the snout. A generalized type is one with fewer 

 pecuHarities, as the herring in comparison with the sculpin. In 

 the process of evolution generalized types usually give place to 

 specialized ones. Generalized types are therefore as a rule 

 archaic types. The terms high and low are also relative, a 

 high type being one with varied structure and functions. Low 

 types may be primitively generalized, as the lancelet in com- 

 parison with all other fishes, or the herring in comparison with 

 the perch, or they may be due to degradation, a loss of struc- 

 tures which have been elaborately specialized in their ancestry. 

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

 and fins deteriorated is an example of a low type which is spe- 

 cialized as well as degraded. 



High and Low Forms. — In the earlier history of ichthyology 

 much confusion resulted from the misconception of the terms 

 "high" and "low." Because sharks appeared 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. The teleost is adapted to its mode of life, 

 and to that end it is specialized in fin and skeleton rather than 

 in brain and nerves. All degeneration is associated with spe- 

 cialization. The degeneration of the bhndfish is a specializa- 

 tion 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 globefish 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 



