134 



VERTEBRATE ZOOLOGY 



creature. The fins are shaped much as in teleosts, resembling those 

 of the pickerel. The scales are rhombic and heavily coated with ga- 

 noin, so as to make a complete coat of mail. 



The " Bow-fin," Amia calva (Fig. 72, B), or " fresh-water dog- 

 fish," is quite like a typical teleost in form, and would readily pass 

 for a member of that group, except for certain minor ganoid features. 

 Amia is a voracious, carnivorous fish, living in central and southern 

 North America. Its most salient characters are : its continuous dor- 



FIG. 72. Holostei. A, Short-nosed Gar Pike, Lepidosleus platystomus (after 

 Goode). B, The Bow-Fin, Amia calva (after Bridge). 



sal fin (from which its name, " bow-fin" is d^ived) ; its heavy ganoin- 

 covered, imbricating scales; its hompceroal -(really modified hetero- 

 cercal) tail-fin. It has a cellular air-bladder which it uses as a lung, 

 coming frequently to the surface to gulp air. Amia breeds in May 

 and June, building a nest in water weeds, in which it lays its eggs and 

 which the male guards until the eggs hatch. Even after hatching 

 the young remain in a school about the male, who appears to exercise 

 some degree of parental care over them. The egg of Amia is a primi- 

 tive one and the cleavage is holoblastic or nearly so, the whole de- 

 velopment being more like that of an amphibian than like that 

 of a teleost. 



