598 REPRODUCTION. 



of this part of the canal.* The vitellus is thus fecundated immediately 

 upon its discharge from the ovary, and before it has become surrounded 

 with the albuminous envelopes supplied by the oviduct. 



Lastly, in man and mammalians, where the impregnated egg is 

 retained within the body of the female during the whole of its devel- 

 opment, the spermatic fluid is introduced into the vagina and uterus 

 by sexual congress, and meets the egg at or soon after its discharge 

 from the ovary. A close correspondence between the periods of sexual 

 excitement, in the male and the female, is visible in many of these ani- 

 mals, as well as in fish, birds, and reptiles. This is the case in most 

 species which produce young but once a year, as the deer, the wolf, 

 and the fox. In others, such as the dog, the rabbit, and the guinea-pig, 

 where several broods of young are produced annually, or where, as in 

 man, the generative epochs of the female recur at short intervals, the 

 time of impregnation is comparatively indefinite, and the generative 

 apparatus of the male is almost constantly in full development. It is 

 excited to action at particular periods, apparently by some influence 

 derived from the condition of the female. 



In quadrupeds and in man, the contact of the sperm with the egg, 

 and the fecundation of the latter, take place in the generative passages 

 of the female ; either in the uterus, the Fallopian tubes, or on the sur- 

 face of the ovary in each of which situations the spermatozoa have 

 been found after sexual intercourse. 



* Foster and Balfour, Elements of Embryology. London, 1874, p. 21. 



