54 



The Skeleton of the Fish 



:\Iost of the fishes with spines in the fins have thoracic ven- 

 trals. In the fishes with jugular ventrals these fins have begun 

 a process of degeneration by which the spines or soft rays or 

 l-)oth are lost or atrophied. 



Degeneration. — By degeneration or degradation in biology 

 IS meant merely a reduction to a lower degree of complexity 

 or s]:)ecialization in structure. If in the process of development 



Fig. 39. — Lower jaw and palate of Sebastolobus alascanits. (After Starks.) 



VA. Palatine. 



MSPT. Mcsopterj'goid. 



PT. Pterygoid. 



MPT. Jletaptcrygoid. 



D. Dentarv. 



AR. Articular. 



.\N. Angular. 



Q. Quadrate. 



SY. ^^^^^lplectic. 



HM. Hvoniandibtilar. 



POP. Preopercle. 



lOP. Interopercle. 



SOP. Subopercle. 



OP. Opercle. 



of the individual some particular organ loses its complexity it 

 is said to be degenerate. If in the geological history of a type 

 the same change takes place the same term is used. Degenera- 

 tion in this sense is, like specialization, a phase of adaptation. 

 It dues nr)t imply disease, feebleness, or mutilation, or any ten- 

 dency toward extinction. It is also necessary to distinguish 

 cleark.' phases of primitive simplicity from the apparent sim- 

 filieity resulting from degeneration. 



The Skeleton in Primitive Fishes.- -To learn the names of bones 

 AA-e can deal most satisfactorily with the higher fishes, those in 



