736 GENERATION AND DEVELOPMENT. 



conditions, provided the natural density of the fluid is pre- 

 served ; disturbing this condition, by either evaporating 

 the semen or diluting it, will stop the movement. It 

 may continue within the body of the female for seven or 

 eight days, and out of the body for at least nearly twenty- 

 four hours. The direction of the movement is quite un- 

 certain : but in general, the current that each excites 

 keeps it from the contact of others. The rate of motion, 

 according to Yalentin, is about one inch in thirteen 

 minutes. 



Eespecting the purpose served, by these seminal fila- 

 ments, or concerning their exact nature, little that is 

 certain can be said. Their occurrence in the impregnating 

 fluid of nearly all classes of animals, proves that they are 

 essential to the process of impregnation ; but beyond this, 

 and that their contact with the ovum is necessary for its 

 development, nothing is known. 



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 vesiculse seminales, 

 whence, if not expelled in emission, it may be discharged, 

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

 may remove minute quantities, mingled with the mucus of 

 the bladder and the secretion of the prostate, or from the 

 urethra in the act of defecation. 



The vesicula seminales have the appearance of out-growths 

 from the vasa deferentia. Each vas deferens, just before 

 it enters the prostate gland, through part of which it 

 passes to terminate in the urethra, gives off a side-branch, 

 which bends back from it at an acute angle; and this 

 branch dilating, variously branching, and pursuing in both 

 itself and its branches a tortuous course, constructs the 

 vesicula seminalis. Each of the vesiculse, therefore, might 

 be unravelled into a single branching tube, sacculated, 

 convoluted, and folded up. 



