PISCES 137 



most elaborate color schemes. Many teleosts are characterized by 

 exaggeration in the development of the fins, both median and paired; 

 others have the snout and jaws over- or underdeveloped for some 

 pecuUar feeding processes. Peculiar breeding habits are accompanied 

 by odd and unique speciaUzations, like the brood-pouches in male 

 pipe-fishes and sea-horses, and the ovipositor by means of which the 

 female Khodeus amarus deposits her eggs in the mantle cavity of the 

 clam Unio, where they develop safely and in a well aerated environ- 

 ment (Fig. 73). Perhaps, however, the most extreme special adapta- 

 tions are those seen in deep-sea fishes of a number of teleost families 

 (Fig. 74) . Two main types are developed, the swift moving types that 

 hunt their prey and the sluggish forms that lie in wait. These fishes, 

 through the use of certain physical principles not yet fully under- 

 stood, are able to resist the pressure of thousands of tons of water and 

 to maintain life at temperatures just above freezing and in the practi- 

 cally total absence of light. In compensation for this life in the dark- 

 ness they are provided with a great variety of phosphorescent organs 

 that enable them to find their way about. 



The Teleost Sub-Okders 



The classification of the immense order Teleostei is a matter about 

 which there is no consensus of opinion. The various subdivisions 

 such as the Acanthopterygii or Malacopterygii are given full ordinal 

 value by Jordan, and merely subordinal value by Boulenger. The 

 present writer, on the basis of extensive hybridization experiments 

 with nimierous species of teleosts, is inclined to believe that these sub- 

 orders should be given, at the most, family value; for, the fact that any 

 two species of teleost can be crossed without artificial aids indicates 

 that they are fundamentally not very distantly related. The thir- 

 teen sub-orders of Boulenger will be briefly surveyed, especial empha- 

 sis being given to those groups that are economically important or 

 phylogenetically significant. Certain types that are either markedly 

 generalized or strikingly specialized will receive attention to the ex- 

 clusion of a large number of types interesting primarily to the spe- 

 cialist. 



Primitive Teleosts {Malacopterygii). — ^This sub-order contains 

 a very large number of species belonging to the Isospondyli and 

 Scyphophori of Cope. About the Isospondyli Jordan says: — "Of 

 the various subordinate groups of fishes, there can be no ques- 



