440 



REPRODUCTION AND DEVELOPMENT 



elements merely, but by the whole generative process. It is one of the 

 most basal instincts of the adult female to be fertilized, just as it is of 

 the adult male to fertilize. Next to that of self-preservation this is the 



FIG. 252 



FIG. 253 



The development of a spermatic! into Cd. 

 spermatozoon. Figs, a to f: Zs, cyto- 

 plasm; A;, nucleus; PC, proximal centro- 

 some; DC, distal centrosome; SF, tail- 

 thread. Fig. g: Sk, head; Ekn, end- 

 nodule; Vst, connecting-part; Hst, chief 

 part; and Est, end-part of the tail. (Meves.) 



strongest of all our instincts, the 

 cause of untold happiness and 

 often the occasion of unimagined 

 misery and crime. 



The male elements of the seeds 

 are deposited either at the en- 

 trance to the uterus or slightly 

 within its neck. The next in- 

 quiry is how these sperms, two 

 hundred millions or so of which 

 are in every normal deposit of 

 semen, reach the distant ovum iii 

 the further end of the Fallopian 



tube or on the surface of the ovary. The alkaline secretions of the 

 mucosa of the uterus and vagina are adapted to preserving the life of 

 the spermatozoa until they reach the tubes. The spermatozoon is an in- 

 dependent motile cell with a very long and active flagellum (tail). By rapid 



Diagram of the front part of a human sperma- 

 toozon: Cp, head ; Cl, neck ; Cd, tail ; P. a., 

 anterior part of the head; L. Gal., edge of the 

 valve; P. p., posterior part of the head; Nd. a., 

 anterior nodule; Ms. int., mid-part of the neck; 

 Nd. p., posterior nodule; Spir., spiral thread; 

 Inv., involucrum of the .connecting part, P. c.; 

 Mtch., mitochondria; Sb. int., intermediary sub- 

 stance; Ann., annulus; F. pr., chief thread; Inv., 

 involucrum; P. pr., chief part of the tail. 

 (Meves.) 



