i64 HEREDITY 



The dynamical nature of the reproductive process 

 is further illustrated by the vibratile character of the 

 spermatozoa. Their movements, which are both 

 varied and rapid, are described as those of torsion, 

 reptation, fluttering and spiral turnings. A single 

 spermatozoon will move at about the rate of 2 to 3 

 millimetres a minute, the rate of progression varying 

 according to the medium in which it happens to be. 

 The vibratile activity is most evident in the middle 

 and tail portions, and some observers assert that it is 

 originated in those parts ; but it seems more natural 

 to suppose that the movements are due to molecular 

 Evidence vibrations in the head portion — vibrations which are 



of dynamic . . . . , 



elements the direct result of the nervous nutritive impulses 

 sperma- which have led to the production and the discharge 

 of the spermatozoon. One thing is undeniable : 

 spermatozoa are not merely collections of inert 

 matter. They are the embodiment of forces of the 

 most varied nature, the dynamic specialization of 

 every cell in the body of the parents taken together ; 

 and this, it is scarcely necessary to say, is in a certain 

 sense the highest form of specialization it is possible 

 for any tissue to assume. 



The spermatozoa of all the vertebrate animals show 

 the same vibratile activity. In crustaceans there is 

 an apparent lack of mobility, which, however, is said 



seems probable that the plexuses mentioned — the spermatic, 

 ovarian, and hypogastric, control the whole of the vascular 

 mechanism of these parts ; nor is it unlikely that they govern 

 secretion respectively in the testis or ovary. 



tozoa and 

 ova. 



