THE FEMALE REPRODUCTIVE ORGANS. 847 



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 J^ 



toward the tubes, being 

 guided in their movements 

 very probably by the oppos- 

 ing force of the ciliary con- 

 tractions in the uterus. It ^k^^H 

 is known that the cilia of 



the tubes and uterus con- ' /^ P 8 



tract so as to drive inert { , 



objects toward the vagina 

 and they carry the egg in 



this direction, but the Fi g- 268 Human ovum (Lee, modified from 



. Nagel): n, Nucleus (germinal vesicle) containing 



Spermatozoa, being moved the ameboid nucleolus (germinal spot); d, deu- 



T ,1 .. ,1 . toplasmic zone: p, protoplasmic zone; z, zona 



by the Contractions Of their radiata; s, penvitellin space. 



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- 

 rounded by a layer of follicular epithelium forming the corona ra- 

 diata, which is subsequently lost. The egg proper consists of 

 cytoplasm and a nucleus or germinal vesicle containing a nucleolus 

 or germinal spot. Within the cytoplasm is a definite collection of 

 food material or yolk which is sometimes designated as deutoplasm. 

 The whole structure is surrounded by a membrane known as the 

 zona radiata (Fig. 268) . Before or after the egg reaches the Fallopian 



