Adaptations of Fishes 2 1 3 



held the contrary view, that the forms with the higher numbers 

 were primitive, but the evidence both from comparative anatomy 

 and from palaeontology seems to indicate that among spiny- 

 rayed fishes the forms most ancient, most generalized, and most 

 synthetic are those with about 24 vertebrae. The soft-rayed 

 fishes without exception show larger numbers, and these are 

 still more primitive. This apparent contradiction is perhaps 

 explained by Dr. Boulenger's suggestion that the prevalence of 

 the same number, 24, in the vertebrae of various families of spiny- 

 rayed fishes is due to common descent, probably from Cretaceous 

 berycoids having this number. In this theory, perches, spa- 

 roids, carangoids, chasdodonts, labroids, parrot-fishes, gobies, 

 flounders, and sculpins must be regarded as having a common 

 origin from which all have diverged since Jurassic times. 

 This view is not at all unlikely and is not inconsistent with the 

 facts of palaeontology. If this be the case, the members of these 

 and related families which have larger numbers of vertebrae 

 must have diverged from the primitive stock. The change has 

 been one of degeneration, the individual vertebrae being reduced 

 in size and complexity, with a vegetative increase in their num- 

 ber. At the same time, the body having the greater number of 

 segments is the more flexible though the segments themselves 

 are less specialized. 



The primitive forms live chiefly along tropical shores, while 

 forms with increased numbers of vertebrae are found in all other 

 localities. This fact must be considered in any hypothesis as 

 to the causes producing such changes. If the development of 

 large numbers be a phase of degeneration the causes of such 

 degeneration must be sought in the colder seas, in the rivers, and 

 in the oceanic abysses. What have these waters in common 

 that the coral reefs, the lava crags, and tide-pools of the tropics 

 have not? 



It is certain that the possession of fewer vertebrae indicates 

 the higher rank, the greater specialization of parts, even though 

 the many vertebrae be a feature less primitive. The evolution 

 of fishes is rarely a movement of progress toward complexity. 

 The time movement in some groups is accompanied by degra- 

 dation and loss of parts, by vegetative repetition of structures, 

 and often by a movement from the fish-form toward the eel- 



