724 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



spermatozoa, formiugthe essential part of the sperm, and moving about 

 when in a fresh condition. They consist of an anterior thicker part, the 

 so-called head, and a more attenuated part, or tail. 



The spermatic corpuscules vary both in size and shape. In the 

 " pesci-cani" (Mustelus), the " rase " (Raja), &c, they are larger, with the 

 head more or less fusiform, and the tail more or less spiral (fig. 12). 



In the osseous fishes, the spermatic corpuscules are, as a general rule, 

 smaller, with the head rounder, and the tail quite attenuated and fili- 

 form (fig. 13). 



Pis. 11. 



Fig. 12. 



Fig. 13. 





Fig. 11. Eipc egg of the Pike (E.?0x 

 lucius), seen from above. 



a. Nutritive yolk. 



b. Germinative disk. 



Fig. 13. Spermatic corpuscle. 



a. Head nearly round. 



b. Filiform tail. 



Fig. 12. Spermatic corpuscle. 



a. The elongated head. 



b. The spiral-formed tail. 

 These corpuscles exe- 

 cute rotary move- 



ments 'with their 

 spiral part, while 

 the other part has a 

 trembling, vibrat- 

 ing, and darting 

 motion. 



The fecundation of the egg consists in the entry of the spermatic cor- 

 puscules into the egg (fig. 14), and in the production of a division of the 

 germinative disk, which phenomenon is called the process of segmenta- 

 tion, or furrowing (fig. 15), followed by a series of successive changes, 

 of which the final result is the embryo, which, feeding on the yolk, 

 gradually develops into the perfect fish. 



Fig. 14. 



Fig. 15. 



Fig. 15. Egg after fecundation, during the period 

 of segmentation, or sulcation, of the 

 germinative disk. 



„ _ a. Nutritive volk. 



Fig. 14. Ripe transparent egg of the Rayno 6> Germinative disk, or yolk of evolu- 



( Trc5HJcr=TRACHiNUS kadiatus), with t i 0Dj divided into four segments. 



spermatic corpuscles. 



a. Yolk. 



b. Lump of fat. 



c. Supermatic corpuscles. 



The fecundation of the egg is effected in the " pesci-cani " (3iustehis) 

 and other viviparous species inside the body of the animal, while in 

 the great majority of fish it takes place outside the body in the water, 

 where the male fish, during the spawning-season, pursues the female, 

 squirting his sperm over the eggs ; and this fact makes artificial fecun- 

 dation and pisciculture possible. 



