352 THE CAT. [CHAP. x. 



kidneys, as two small whitish oval masses of tissue, placed one on 

 the inner side of each Wolffian body, and arising as buds from the 

 mesoblast, between the diverging somatopleure and splanchnopleure. 

 Soon the cells of which they are composed become divided by septa 

 of connective tissue, and the cells themselves grow into the tubuli 

 seminiferi. Meanwhile, the tubes of the Wolffian body become 

 approximated to, and ultimately united with, the testis, and form 

 the vasa efferentia and coni vasculosi of the epididymis, the duct of 

 the Wolffian body becoming the vas drferens, some of its detached 

 tubes forming the vas aberrans and Organ of Giraldes.* The testes 

 ultimately descend from the abdominal cavity into the scrotum, 

 which is formed by the median junction of two folds of skin, which 

 grow from the sides of the external opening of the urogenital sinus. 



The penis first appears as a small recurved process projecting 

 from the front margin of the urogenital opening (Fig. 158, A, rp) t 

 consisting of what are to be the corpora cavernosa, with a portion 

 of corpus spongiosum at its distal end and extending down the 

 grooved ventral, or posterior, surface of the developing organ. The 

 lateral margins of this groove grow over and close, so converting the 

 groove into a canal the spongy portion of the urethra. This canal 

 then opens posteriorly into the front end of the urogenital sinus, 

 which still opens externally at the root of the penis, though 

 separated from the anal aperture by a transverse partition, the 

 incipient perineum. By degrees this inferior opening of the uro- 

 genital sinus grows over and closes, and thus the spongy urethra 

 comes to form one continuous tube with the urethra as it quits the 

 bladder, while the posterior end of the ventral surface of the penis 

 becomes continuous with the medianly coalesced lateral folds which 

 have formed the scrotum and invested the place where was the external 

 opening of the urogenital sinus at the root of the developing penis. 



The OVARY arises just as does the testis, and is at first indistin- 

 guishable from it. Soon, however, it comes to differ somewhat in 

 shape, and ova and G-raafian vesicles arise from the very first within 

 it. It does not form the same kind of adhesion to the Wolffian 

 body as do the testes, but its stroma is formed by outgrowth of 

 tissue into it from the Wolffian body. A fibrous cord, the round 

 ligament, comes to connect the ovary with the pubis through the in- 

 guinal ring, but the ovary never passes outside the abdominal cavity, 

 though it descends a little from its primitive position. It becomes 

 wrapped round by the fold of peritoneum, the broad ligament, which 

 is reflected on each side from the uterus, so that no discharge of its 

 contents can take place without rupture of its peritoneal investment. 



The vagina and uterus arise as the partially conjoined hinder 

 ends of the two Mullerian ducts, which open into the dorsal wall of 

 the urogenital sinus (Fig. 158, B). The simple tube comes by 

 degrees to alter in size and structure in different regions, its deeper 

 portion becoming very muscular (as the uterus) and separated from 

 the hinder part, the vagina, by a constriction forming the os uteri 



* See ante, p. 244. 



