REPRODUCTION. 



61 



THE MALE CELL (SPERMATOZOON). 



This cell, almost without exception, consists of a nucleus 

 (head) and vlbratile ciUum. However, as indicating that the 



Fig. 60. — Spennntozoa (after Haddon). Not drawn to scale. 1, sponge; 2, hydroid; 

 3, nematode; 4, cray-fish; 5, snail; 6, electric ray; 7, salamander; 8. horse; 9, man. 

 In many spermatozoa, as in Nos. 7 and 9, an extremely delicate vibratile band is 

 present. 



latter is not essential, spermatozoa without such 5n appendage 

 do occur. The obvious purpose of the cilium is to convey the 

 male cell to the ovum through a fluid medium — either the water 

 in which the ova are discharged in the case of most invertebrates, 

 or through the fluids that overspread the surfaces of the female 

 generative organs. 



The Origin of the Spermatozoon.— The structures devoted to 

 the production of male cells (testes), when reduced to their es- 

 sentials, consist of tubules, of great length in mammals, lined 



