FISHES 



347 



Photograph from Am. Mus. Natural History 

 FIG. 130. Group showing nesting habits of the bowfin. 



scales, though without the well-defined peg-and-socket 

 arrangement. It is to this type that the term " ganoid " 

 has been more especially restricted in recent years. 



The bowfin (Amia caka), also of the Mississippi 

 Valley, is actually nearer to the garpike than the latter 

 is to Polypterus, though its scales are not ganoid. It is, 

 however, a very. distinct and isolated type, and although 

 the scales superficially resemble those of many of the 

 higher fishes, the fine fibrilloe or threads composing the 

 basal part run lengthwise as they do in the lung- 

 fishes. 



The sturgeons (Chondrostei) constitute another iso- sturgeons 

 lated type surviving from ancient times. They have 

 large, bony plates on the body, and the tail is heterocer- 

 cal- - that is to say, bends upward at the end, carrying 

 the fin on the lower side. This is a feature also ob- 

 served in the sharks, and less conspicuously in the 

 bowfin and garpike. It will be noted that these groups 

 of archaic fishes exist in fresh water, in the large river 

 systems of continental areas, but not in the sea. 



