LECTURE VIII. 49 



tirely destitute, the particular kind of stridulous 

 sound which some kinds are observed to produce 

 on being first taken out of the water, being en- 

 tirely owing to the sudden expulsion of air from 

 their internal cavities, as in the Gurnards or Pi- 

 pers, and some other fishes. 



By far the greater number of fishes are ovipa- 

 rous, producing soft eggs, usually known by the 

 name of spawn. Some fishes are however vivi- 

 parous, the eggs first hatching internally. Fishes 

 may certainly be considered as the most prolific 

 of all animals : many millions often proceeding 

 from a single individual. The gradual evolution 

 of the young from the egg is highly curious. In 

 the spawn of the Barbel and some others, which 

 usually hatches in the space of about nine or ten 

 days, on the second day may be perceived in each 

 egg a small dusky speck between the white and 

 the yolk : on the third day the motion or pulsa- 

 tion of the heart becomes visible, and the body 

 may be perceived, adhering laterally to the yolk: 

 on the 6th day the back-bone and ribs are percep- 

 tible ; on the 7th day the eyes ; and the animal 

 begins to move itself briskly from time to time, 

 till at length, on the 9th or 10th day it bursts from 



LECT. ir. E 



