880 THE PHYSIOLOGY OF REPRODUCTION. 



of the corpora lutea, while the embryos are developed in the horn 

 of the other side. As further evidence for the same possibility of 

 migration it has been shown that the ovary may be excised on one 

 side and the horn of the uterus on the other and yet the animal may 

 become pregnant after sexual union. It would seem probable, 

 therefore, that the ovum is discharged into the pelvic cavity and 

 may be caught up by the ciliary movements at the end of the tube 

 on the same side, or may traverse the pelvic cavity in the narrow 

 spaces between the viscera and be received by the tube on the 

 other side. Such a view explains the possible occurrence of true 

 abdominal pregnancies, and suggests also the possibility that ova 

 may at times fail to reach the uterus at all and may undergo de- 

 struction and absorption in the abdominal cavity. In some of 

 the lower animals the dog, for example provision is made for 

 the more certain entrance of the ova into the tubes by the fact 

 that the latter end in connection with a membranous sac of peri- 

 toneum which envelopes the ovary. The sexual fertilization of the 

 ovum is supposed to take place shortly after its entrance into 

 the Fallopian tube, since spermatozoa have been found in this 

 region, and the fertilized ovum, before reaching the seat of its im- 

 plantation in the body of the uterus, has begun its development. 



By the act of coitus the 

 spermatozoa are deposited 

 at the mouth of the uterus, 

 whence they make their way 

 toward the tubes, being 

 __ d guided in their movements 

 very probably by the oppos- 

 ing force of the ciliary con- 

 ~j~ n tractions in the uterus. It 

 is known that the cilia of 

 the tubes and uterus con- 

 tract so as to drive inert 

 objects toward the vagina 

 and they carry the egg in 



Fig. 277. Human ovum (Lee, modified from this direction, b U t the 

 Nagel): n, Nucleus (germinal vesicle) containing enprrrmtn'/nfl hpino* rnnvpH 

 the ameboid nucleolus (germinal spot); d, deu- SpermaiOZOa, I 



radiata niC ZOne rivifellFn sac| SmiC ^^ *' ^^ ^ the cont ractions of their 



own cilia or tails, are 



stimulated to advance against this ciliary current. The act of ferti- 

 lization of the ovum is preceded by certain preparatory changes 

 in the ovum itself which are described under the term maturation. 

 Maturation of the Ovum. The process of maturation occurs 

 before or just after the spermatozoon enters the ovum. At the 

 time the latter is extruded from the follicle it is a single cell sur- 



