386 



COLLEGE ZOOLOGY 



Germina 

 disk 



Embryo of 32 somites 



Early blastoderm 



Yolk 



Blastoderm 

 overgrowing yolk- 



Embryo of 25 somites 



OJI 



Embryo of 18 somites 



Embryo with 

 optic vesicles 



Early embryo 



Figure 258. Early embryology of a bony fish, the goldfish. (After Helen I. Battle, Ohio J. Sci. 

 40:85, 1940.) 



tions in form are correlated with the habits 

 of the fish. For example, flounders (Fig. 

 262) have flat bodies and are adapted for 

 life on the sea bottom; and eels (Fig. 252) 

 have long cylindrical bodies which enable 

 them to enter holes and crevices. 



Fins and tail 



Fins, according to some zoologists, arise 

 in the embryo as median and lateral folds of 

 the integument (Fig. 259), which are at first 

 continuous. Later, parts of the folds disap- 

 pear and the isolated dorsal, caudal, anal. 



