26 David Starr Jordan 



physostomous fishes, the allies of the salmon/'' pike, carp, and 

 cat-fish. In all of these the vertebrae are numerous. A few 

 fresh water families have their affinities entirely with the more 

 specialized forms of the tropical seas. Of these the Centrarchi- 

 dce (comprising the American fresh-water sun-fishf and black 

 bass X) have on the average about 30 vertebrae, the pirate 

 perch § 29, and the perch || family, perch and darters, etc., 35 

 to 45, while the Serranida or sea bass, the nearest marine rel- 

 atives of all these, have constantly 24. The marine family of 

 demoiselles^ have 26 vertebrae, while 30 to 40 vertebrae 

 usually exist in their fresh-water analogues (or possibly de- 

 scendants), the Cichlidce, of the rivers of South America and 

 Africa. The sticklebacks,** a family of spiny fishes, confined 

 to the rivers and seas of the north, have from 31 vertebrae to 

 41. The Ophiocephalida;, A?tabantidce and other old world 

 families of fresh water fishes have more vertebrae than their 

 marine analogues. No fresh water fishes (except a few Sciceni- 

 dcB,'\^ which have come comparatively recently into fresh 

 waters) have the number of vertebrae as low as 24, the usual 

 number in the spiny-rayed shore fishes of the tropics. 



Pelagic Fishes. — It is apparentl}^ true that among the free 

 swimming, or migratory pelagic fishes, the number of verte- 

 brae is greater than among their relatives of local habits. 

 This fact is most evident among the scombriform fishes, the 

 allies of the mackerel and tunny. All of these belong prop- 

 erly to the warm seas, and the reduction of the vertebrae in 

 certain forms has no evident relation to the temperature, 

 though it seems to be related in some degree to the habits 

 of the species. Perhaps the retention of many segments is 

 connected with that strength and swiftness in the water for 

 which the mackerels are preeminent. 



The variations in the number of vertebrae in this group led 

 Dr. Giinther, nearly 30 years ago, to divide it into two 

 families, the Carangidoe and Scombridoe. 



* Cyprinidos, Salmonidce, Esocidos, Characinidce, Cyprinodontidce , 

 Siluridce, etc. 



■\ Lepomis. \ Pomacentridce. \Percidce. 



I Aphredoderidce. \ Micropterus. ** Gasterosteidce. 



ft Aplodinotus Plagioscion Pachyurus, etc. 



