654 HANDBOOK OF PHYSIOLOGY. 



vitality becomes impaired the motion gets slower, and it is then easily 

 perceived to be a continuous waving from side to side. 



The spermatozoa of all Mammalia examined, consisting of Man, 

 Bull, Dog, Horse, Cat, Pig, Mouse, Rat, Guinea-pig, had, instead of 

 the long-pointed head of the Amphibian, a blunt thick process of dif- 

 ferent shapes in the different animals: and from the root or neck of this 

 proceeded the long filament, just as in the Amphibia, only so delicate as 

 to be invisible except with very high powers. 



In Man the head (Fig. 441) is club-shaped, and from its base springs 

 the very delicate filament, which is three or four times as long as the 

 body; and the membrane which attaches it to the body is much broader, 

 and" allows it to lie at a greater distance from the body than in the 

 spermatozoa of any other Mammal examined. 



From his investigations, Gribbes concluded: 1st. That the head of 

 the spermatozoon is inclosed in a sheath, which is a continuation of the 

 membrane which surrounds the filament, and connects it to the body, 

 acting in fact the part of a mesentery. 2dly. That the substance of the 

 head is quite distinct in its composition from the elliptical structure, the 

 filament and the long body, and that it is readily acted on by alkalies; 

 these reagents have no effect, however, on the other part, excepting the 

 membranous sheath. 3dly. That this elliptical structure has its ana- 

 logue in the Mammalian spermatozoon, in the one case the head is 

 drawn out as a long pointed process, in the other it is of a globular 

 form, and surrounds the elliptical structure. 4thly. That the motive 

 power lies, in a great measure, in the filament and the membrane attach- 

 ing it to the body. 



The spermatozoa are derived from the breaking up of the seminal 

 cells or daughter cells. They must be looked upon as modified cells. 



The occurrence of spermatozoa in the impregnating fluid of nearly 

 all classes of animals, proves that they are essential to the process of im- 

 pregnation, and their actual contact with the ovum is necessary for its 

 development. 



The seminal fluid is, probably, after the period of puberty secreted 

 constantly, though, except under excitement, very slowly, in the tubules 

 of the testicles. From these it passes along the vasa deferentia into the 

 vesiculae seminales, whence, if not expelled in emission, it may be dis- 

 charged, as slowly as it enters them, either with the urine, which jnay 

 remove minute quantities, mingled with the mucus of the bladder and 

 the secretion of the prostate, or from the urethra in the act of defe- 

 cation. 



To the vesiculae seminales a double function may be assigned: for 

 they both secrete some fluid to be added to that of the testicles, and serve 

 as reservoirs for the seminal fluid. The former is their most constant 

 and probably most important office; for in the horse, bear, guinea-pig, 

 and several other animals, in whom the vesiculae seminales are large and 

 of apparently active function, they do not communicate with the vasa 

 deferentia, but pour their secretions, separately, though it maybe simul- 

 taneously, into the urethra. In man, also, when one testicle is lost, the 



