64 FISH CULTURE. 



the ova; but, at length, globules of an oily-looking 

 substance are formed. By degrees, these densify, 

 and, by aid of a strong glass, a thin whitish line 

 may be traced coiled within the egg. This is the 

 earliest development of the spinal column, and of 

 course it becomes more distinct as the animal becomes 

 more formed. And about the fifth or sixth week (in 



water of moderate temperature, we may say, usually 

 from the thirty-fifth to the forty-fifth day), a small 

 dark speck, probably, on close examination, two 

 black specks, will be observable. These are the eyes 

 of the embryo, the form of which may now be traced 

 almost by the naked eye. In a few more days, the 

 eyes become distinct, and the embryo may be dis- 

 cerned without the aid of a glass, moving and often 



