Temperature and Vertebra 35 



But while claiming the generalization that there is a correlation be- 

 tween the increase of vertebrae and the increase of latitude among 

 fishes, I would not assign it an undue value or claim for it the dignity 

 of a law. It is simply the expression of a fact which has no cause for 

 its being now known. It may be added that this generalization is true 

 only in a general sense. 



Jo>'da7i, 1S91. — In another paper* the present writer has., 

 said ; 



This increase in the number of vertebrae in northern forms has been 

 used as a basis of classification of the Pleuronedidcc by Jordan and 

 Goss, of the Scorptznidce by Jordan and Gilbert, and it will doubtless. 

 prove to have a high value in the subdivision of other families which 

 have representatives in different zones. The cause of this peculiarity of 

 fishes of cold waters is still obscure. Probably the reduction in num- 

 ber of segments is a result of the specialization of structure incident to 

 the sharper competition of the tropical waters, where the outside con- 

 ditions of life are very favorable for fishes, but the struggle of species 

 against species is most severe. 



In this paper is given a table which shows that in the 

 genera of Labridce f inhabiting northern E.urope and the New 

 England waters there are 38 to 41 vertebrae, in the Mediter- 

 ranean forms :|: 30 to 33, in certain subtropical genera § 27 to 

 29, while in those Labroids which chiefly abound about the 

 coral reefs || the number is from 23 to 25. 



Jordan & Eigenmann, 189.1.^ — ^In a recent paper on the 

 Serranidcz (sea-bass and groupers) it is stated, that the group 

 as a whole belongs to the tropical seas, and that it differs from 

 the related fresh- water family of Percidcehy the much smaller 

 number of vertebrae, usttally 24, which is the number most 

 common among spiny-rayed fishes. Among the Serranidce, 

 however, two genera form exceptions to the general rule. 

 One of these, ** with 35 vertebrae, occurs in the rivers of 

 China, the other, ff with 36 vertebrae, in the mountain streams 



* Review of the Ivabroid Fishes of America and Europe, p. 2. 



t Labrus, Acantholabrus, Ctenolabrus, Tautoga. 



X Chiefly belonging to Symphodus. § Lachnolaimus, Harpe, etc. 



\ Scams, Sparisoma, Xyrichthys, Jiilis, Thalassoma, etc. 



1[ A Review of the Genera and Species of Serranidce found in the 

 waters, of America and Europe, by David S. Jordan and Carl H. Eigen- 

 mann. 



** Lateolabrax. ft Percichthys. 



