562 MALE ORGANS OF GENERATION. 



the two sexes and the operation of corresponding instincts, leading 

 them to ascend the same rivers and to frequent the same spots, 

 provide with sufficient certainty for the impregnation of the eggs. 

 In these animals, also, the number of eggs produced by the female 

 is very large, the ovaries being often so distended as to fill nearly 

 the whole of the abdominal cavity ; so that, although many of the 

 eggs may be accidentally lost, a sufficient number will still be im- 

 pregnated and developed, to provide for the continuation of* the 

 species. 



In other instances, an actual contact takes place between the 

 sexes at the time of reproduction. In the frog, for example, the 

 male fastens himself upon the back of the female by the anterior 

 extremities, which seem to retain their hold by a kind of spasmodic 

 contraction. This continues for one or two days, during which 

 time the mature eggs, which have been discharged from the ovary, 

 are passing downward through the oviducts. At last they are ex- 

 pelled from the anus, while at the same time the seminal fluid of 

 the male is discharged upon them, and impregnation takes place. 



In the higher classes of animals, however, and in man, where the 

 egg is to be retained in the body of the female parent during its 

 development, the spermatic fluid is introduced into the female 

 generative passages by sexual congress, and meets the egg at or 

 soon after its discharge from the ovary. The same correspondence, 

 however, between the periods of sexual excitement in the male and 

 female, is visible in many of these animals, as well as in fish and 

 reptiles. This is the case in most species which produce young but 

 once a year, and at a fixed period, as the deer and the wild hog. In 

 other species, on the contrary, such as the dog, as well as the rabbit, 

 the guinea pig, &c., where several broods of young are produced 

 during the year, or where, as in the human subject, the generative 

 epochs of the female recur at short intervals, so that the particular 

 period of impregnation is comparatively indefinite, the generative 

 apparatus of the male is almost constantly in a state of full deve- 

 lopment ; and is excited to action at particular periods, apparently 

 by some influence derived from the condition of the female. 



In the quadrupeds, accordingly, and in the human species, 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 even upon the surface of the ovary ; 

 in each of which situations the spermatozoa have been found, after 

 the accomplishment of sexual intercourse. 



