12 Veterinary Obstetrics 



which, however, only divides after conjugation and fusion with 

 the male cell, the spermatozoon, while the parental body remains 

 unchanged after the separation and casting off of the male or 

 female reproductive cell. 



The ova-producing bodies, the ovaries, appear early during 

 embryonic life, varying in date according to species — usually at 

 about one month in those of long gestation periods. The first 

 traces of the ovaries are the genital ridges, which arise as longitud- 

 inal eminences along the median borders of the Wolffian bodies 

 and consist of a proliferation of the peritoneal epithelium at this 

 point, by which several layers of cells are formed. The ridges 

 appear in the human embryo at about 35 days or one-eighth 

 term, in the rabbit at ii days or a trifle after the first one-third, 

 and in the sheep at 42 days or nearly one-half term. 



Connective tissue grows up into the genital ridges from the 

 underlying mesoblastic cells to form the skeletal frame- work and 

 tubules from the Wolffian bodies grow into the ridges to consti- 

 tute the tubular tissue of the ovary, but they play no known 

 essential part and are said to have nothing to do with the forma- 

 tion of the ova. For a time the genital ridges are alike in both 

 sexes, so far as can be determined, forming the indifferent stage 

 during which the male and female organs cannot be differentiated. 



As the genital ridges develop, the differentiation in sex becomes 

 established and, in the female, the ovary soon assumes the charac- 

 teristic form of the adult, varying with the species. 



While it is held that all ovarian tissues are of mesoblastic ori- 

 gin, the genital epithelium, arising from the peritoneum, the 

 skeletal connective tissue frpm the sub-peritoneal mesoblast and 

 the tubular portion from the mesoblastic Wolffian bodies, we meet 

 with in various animals, especially in the horse and human fam- 

 ily, dermoid cysts and well defined tooth tissues in the ovaries 

 and testicles. These abnormalities are variously explained by 

 pathologists and teratologists. Since dermal structures and teeth 

 are derived normally from the epiderm, it may be well to recall 

 in this connection that the gubernaculum testis of the male and 

 corresponding round ligament of the female extends from the ex- 

 ternal skin in the scrotal region of the male and the correspond- 

 ing parts in the female through the inguinal canal and ring into 

 the peritoneal cavity, where it proceeds to a point contiguous to, 

 if not continuous with, the testicle or ovary. Embryologists do 



