THE MALE ORGANS OF GENERATION. 595 



vesiculae seminales into the prostatic portion of the urethra, where it 

 meets with the secretion of the prostate gland, then poured out in 

 unusual abundance ; and farther on, there are added the secretions of 

 Cowper's glands and of the remaining mucous follicles of the urethra. 

 All these increase the volume of the spermatic fluid, and serve as 

 vehicles for the transport of the spermatozoa, 



Conditions of Fecundation by the Spermatic Fluid. There are 

 several conditions which are essential to the accomplishment of fecun- 

 dation. 



First, the spermatozoa must be present and in a state of vitality. 

 Of all the organic ingredients, derived from different sources, which 

 go to make up the spermatic fluid, the spermatozoa form the essential 

 part. They are the fecundating element of the sperm, while the rest 

 perform only accessory functions. 



Spallanzani * found that if frog's sperm be passed through a succes- 

 sion of filters, so as to separate the solid from the liquid portions, the 

 filtered fluid is destitute of fecundating properties ; while the sperma- 

 tozoa entangled in the filter, if mixed with a sufficient quantity of 

 fluid, may be successfully used for the impregnation of eggs. The 

 removal of both testicles destroys the power of impregnating the 

 female, notwithstanding that all the other generative organs may 

 remain uninjured. The spermatic fluid, furthermore, must be in a 

 fresh condition, and the spermatozoa must retain their anatomical 

 characters and their active movement. The experiments of Spallan- 

 zani have shown that, if the above conditions be preserved, the fluid, 

 removed from the spermatic ducts of the male, is capable of fecun- 

 dating the eggs of the female. But if exposed for a certain time to 

 the atmosphere, or to unnatural temperatures, it becomes inert. So 

 long as the spermatozoa continue in active motion, they are usually 

 found to retain their physiological properties ; the cessation of move- 

 ment indicating that their vitality is exhausted, and that they are no 

 longer capable of impregnating the egg. 



Secondly, both eggs and spermatozoa must have arrived at a certain 

 degree of development before fecundation can take place. Previous to 

 this time the immature eggs are incapable of being impregnated, and 

 the imperfectly developed spermatozoa have not yet acquired their 

 fecundating power. The necessary growth takes place within the 

 generative organs ; and when it is complete, both spermatozoa and 

 eggs are ready to be discharged, and are in condition to exert and 

 receive the necessary influence. 



The fecundating power of the spermatozoa is exceedingly active. 

 Spallanzani found one-fifth of a gramme of the spermatic fluid of the 

 frog, diffused in water, sufficient for the impregnation of several thou- 

 sand eggs. The process seems to be accomplished almost instanta- 

 neously, " since eggs which were allowed to remain in the fecundating 



* Experiences pour servir a 1'Histoire de la Generation. Geneve, 1786. 



