Adaptations of Fishes 207 



farther south, Lophiomus setigerus, the vertebrae are but IQ. 

 Yet in external appearance these two fishes are almost iden- 

 tical. It is, however, a notable fact that some of the deep-water 

 Pediculates, or angling fishes, have the body very short and the 

 number of vertebras correspondingly reduced. Dibranchus atlan 

 ticus, from a depth of 3600 fathoms, or more than 4 miles, has 

 but 1 8 vertebrae, and others of its relatives in deep waters show 

 also small numbers. These soft-bodied fishes are simply ani- 

 mated mouths, with a feeble osseous structure, and they are 

 perhaps recent offshoots from some stock which has extended 

 its range from muddy bottom or from floating seaweed to the 

 depths of the sea. 



A very few spiny-rayed families are wholly confined to the 

 northern seas. One of the most notable of these is the family 

 of viviparous surf -fishes (Embiotocidaz) , of which numerous species 

 abound on the coasts of California and Japan, but which enter 

 neither the waters of the frigid nor of the torrid zone. The surf- 

 fishes have from 32 to 42 vertebrae, numbers which are never 

 found among tropical fishes of similar appearance or relation- 

 ship. 



The facts of variation with latitude were first noticed among 

 the Labrida. In the northern genera (Labrus, Tautoga, etc.) 

 there are 38 to 41 vertebrae; in the semitropical genera (Creni- 

 labrus, Bodianus, etc.), 30 to 33; in the tropical genera (Hali- 

 chceres, Xyrichthys, Thalassoma, etc.), usually 24. 



Equally striking are the facts in the great group of Pareio- 

 plita, or mailed-cheek fishes, composed of numerous families, 

 diverging from each other in various respects, but agreeing in 

 certain peculiarities of the skeleton. 



Among these fishes the family most nearly related to ordi- 

 nary fishes is that of the Scorp&nida (scorpion-fishes, etc.). 



This is a large family containing many species, fishes of local 

 habits, swarming about the rocks at moderate depths in all 

 zones. The species of the tropical genera have all 24 vertebrae. 

 Those genera chiefly found in cooler waters, as in California, 

 Japan, Chile, and the Cape of Good Hope, have in all their species 

 2 7 vertebrae, while in the arctic genera there are 3 1 . 



Allied to the Scorpcenida, but confined to the tropical or 

 semitropical seas, are the Platycephalida, with 27 vertebrae, and 



