SEX IN LIVING FORMS 91 



Human spermatozoa are about one-six-liundredth 

 of an inch in length. Those of reptiles are very much 

 larger. One of the remarkable features of these mi- 

 nute elements is their peculiar movements. While 

 alive, the filamentous tail is in constant action in a 

 manner strongly resembling the movements of the cau- 

 dal appendage of a tadpole. This wonderful property 

 led the earlier observers to believe that they were true 

 animalcula. But they are not to be regarded as such, 

 though one can scarcely make himself believe other- 

 wise while watching their lively evolutions, and ap- 

 parently volitionary movements from one point to 

 another. 



Spermatozoa originate in the testis as cells, which 

 are filled with granules. After a time, each granule 

 acquires a long appendage, and then the cell has be- 

 come converted into a bundle of small zoosperms. 

 Development still continues, until finally the thin pel- 

 licle on the outside of the bundle is ruptured, thus lib- 

 erating the spermatozoa, which speedily complete their 

 full development. The spermatozoon is pure proto^ 

 plasm, which is the basis of all life, and its power of 

 spontaneous motion is due to this fact. 



In man, the formation of spermatozoa continues 

 with greater or less rapidity from puberty to old age, 

 though at the two extremes of existence they are im- 

 perfectly developed. When not discharged from the 

 body, they are said to be absorbed. 



It is asserted by good authorities that the repro- 

 ductive element in man is not sufficiently developed to 

 be really fit for the reproduction of the species before 

 the age of twenty-four or twenty-five. After the age 

 of fifty, this element deteriorates in quality, and is 

 again unfitted for vigorous procreation. 



