GANOID FISHES 



637 



nest of grasses within which the eggs are laid and develop. The eggs 

 are a little over a millimetre in diameter. They hatch into larvae 

 resembling the larva3 of Dipnoans and Amphibians, with a pair of large 

 feathery external gills and a glandular sucker on the underside of the 

 head, by which the young Polypteru'^ adheres to waterplants in tad- 

 pole-like fashion. Polypterus, and Calamoichtkys, which lacks pelvic 

 fins and is eel-like in form, are archaic fishes of great interest to the 

 student of vertebrate morphology. 



Pig. 363. — Polypterus bichir. — From a Specimen. 



D.F., Interrupted dorsal tins; P.F., pelvic fin; PE.F., pectoral fin, 

 with characteristic strong basal portion ; C.F., caudal fin ; I .t ., 

 unpaired ventral fin. 



The following three orders are often grouped as 

 Actinopterygii, in reference to the fins which, in contrast 

 to the Crossopterygian fin, are never lobate, but have short 

 basal pieces and are mainly supported by dermal fin-rays. 



Fig. 364.— Larva of Polypterus (after Budgett), i\ inch in length. 



e.g Large external gill of the hyoid arch ; Pc., pectoral fins ; Pv., pelvic 

 fins. The larva is drawn in a very characteristic attitude. 



Order 2. Chondrostei — with cartilaginous 

 internal skeleton 



living examples : — Sturgeon {Acipenser), Polyodon, Sca- 

 phirhynchus. Extinct examples : — Cheirolepis, Palce- 

 oniscus, Chondrosteus. 



