MALE ORGANS OF GENERATION 699 



if the above conditions be preserved, the seminal fluid, removed from 

 the spermatic ducts of the male, is capable of fecundating the eggs of 

 the female. But if allowed to remain exposed to the atmosphere, or to 

 an unnatural temperature, it becomes inert. So long as the spermatozoa 

 continue in active motion, they are usually found to retain their physio- 

 logical properties ; the cessation of this movement, on the other hand, 

 being a sign 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 fecun- 

 dating power. The necessary process of growth takes place within the 

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

 the male and the eggs of the female are ready to be discharged, and are 

 in condition to exert upon each other the necessary influence. 



The fecundating power of the spermatozoa, when fully developed, is 

 exceedingly active. Spallanzani found that one-fifth of a gramme of 

 the seminal fluid of the frog, diffused in water, was sufficient for the 

 impregnation of several thousand eggs. The process seems to be ac- 

 complished almost instantaneously, " since eggs which were allowed to 

 remain in the fecundating mixture for only one second proved to be 

 impregnated, and were afterward hatched at the usual period." 



Thirdly, the spermatozoa must come into direct contact with the egg 

 or its immediate envelopes. Spallanzani first demonstrated this by 

 attaching mature eggs to the concave surface of a watch-glass, which 

 he placed, in an inverted position, over a second watch-glass containing 

 fresh seminal fluid. The eggs, allowed to remain in this way for several 

 hours, exposed to the vapor of the fluid but without touching its surface, 

 were afterward found to have failed of impregnation ; while others, which 

 were actually moistened with the same seminal fluid, became developed 

 into living tadpoles. 



Finally, the physiological act of fecundation is accomplished by the 

 entrance of the spermatozoa into the interior of the egg, through the 

 vitelline membrane, and their union with the substance of the vitellus. 

 This fact was first observed by Martin Barry 1 in the fecundated egg 

 from the Fallopian tube of the rabbit. It has subsequently been seen 

 by Newport 2 in the frog, by Bischoff, by Coste, by Robin 3 in a species of 

 leech, by Flint 4 in the pond snail, and by Weil, 5 in repeated instances, in 

 the rabbit. According to some of these observations, the mechanism of 

 penetration is by means of a natural orifice or " micropyle" existing in 



1 Philosophical Transactions. London, 1840, p. 533, and 1843, p. 33. 



2 Philosophical Transactions, 1853, p. 271. 



3 Journal de la Physiologic de 1'Homme et des Animaux. Paris, 1862, tome 

 v. p. 80. 



4 Physiology of Man. New York, 1874, vol. v. p. 352. 



6 Strieker's Medizinischer Jahrbucher. Wien, 1873, p. 18. 



