Fish Life. 



43 



large, quiescent, and contains a large 

 amount of nutriment, which goes towards 

 the formation of at least tlic first stages 

 of the young animal. It is usually spher- 

 ical, or nearly so, in form. 



The sperm-cell is small, active, contains 

 very little nutritive material, and is gener- 

 ally composed of a larger part or "head," 

 and a long slender contractile " tail," 

 " which," we are told, " working behind 

 like a screw, propels the essential head 

 through the water or along the ducts." 



Some of the forms of the sperm-cell are 

 drawn at the side of the page; beginning 

 at the top and reading down, they are : 

 thread-worm, crayfish, sponge, lobster, 

 crab, dog, rabbit, mouse, dog, pig. 



The sperm-cell of the human being is 

 of the same nature, consisting of a blunt, 

 oblong " head," and a long, slender, whip- 

 like portion. 



Thus, while the egg-cells of different 

 creatures are constant in form, differing 

 mainly in the amount of nutriment they 

 store up, the sperm-cells are extremely 

 variable, and while the " head " and " tail " 

 characterize those of most animals, " occa- 

 sionally," we are told, " there is a depart- 

 ure from the predominant phase of cell- , 

 life. Thus in the thread-worm, the sperm 



