CLASS PISCES 



345 



369. Chondrostei. — In the Chondrostei, or cartilaginous ganoids, 

 the pelvic fins are not used to support the body, and the tadpole-like 

 larva has been considerably modified. The skeleton is largely car- 



FiG. 232. — A crossopterygian, Polyptenis senegalus Cuvier a, the adult. X J^. 

 6, the larva. X 2%. {a from Bridge, ''Cambridge Natural History,'" b after Budgett, by 

 the courtesy of The Macmillan Company.) The latter figure does not show the fact that 

 the gills are alternately long and short. The arrow and line in Fig. a point to the position 

 of the left spiracle. 



tilaginous, but the cartilage is overlaid with dermal bones. The sturgeons 

 (Fig. 233) are examples of this group. 



Fig. 2.33. — Lake sturgeon, Acipenser rubicundus LeSueur. X Ms- (From, Jordan, 

 "Guide to the Study of Fishes," by the courtesy of D. Appleton & Company.) 



370. Holostei. — The Holostei, or bony ganoids, have a completely 

 ossified skeleton. In some the scales form a complete armor. Examples 



Fig. 234. — Alligator gar, Lepiaosteus tristoechus (Block and Schneider). X J^o- (From 

 Jordan, "Guide to the Study of Fishes," by the courtesy of D. Appleton & Company.) 



are the fresh-water dogfish, or bowfin, and the gars and gar pikes (Fig. 

 234). The development of the bowfin betrays primitive characteristics. 

 The eggs are nearly holoblastic, and the early development is rather more 



