THE URINOGENITAL SYSTEM 189 



In the wholly vestigial condition the mesonephros is not infrequently 

 the seat of origin of pathological affections (formation of cysts). 



The vestigial portions of the mesonephros in men are 

 the paradidymis, Giralde"'s organ, and the stalked hydatids of 

 x -Morgagni; in women it gives rise to the greater part of the 

 parovarium and the whole of the paroophoron. Further, in 

 women, the last vestiges of its duct are found, either confined to 

 the region of the parovarium, or, where suppression is least 

 marked, in the form of "Gartner's canal" which reaches the vagina. 



MiJLLERIAN DUCT 



Van Wijhe, believing that the ancestors of the vertebrate were 



hermaphrodite, has argued that the first appearance of the Mullerian 



duct probably dates back to a period in the evolution of the phylum 



when, as a means of preventing self - fertilisation, there were 



distinct ducts for the transmission of the sperm and the ova. Be 



this as it may, the secondary nature of the Miillerian duct is 



shown by its comparatively late development in the individual. 



' It originates in the Amniota by evagination of the ccelomic 



I epithelium, to form a structure which, becoming constricted off 



\ into a tube, gradually elongates in a caudal direction to reach 



the cloaca. 



In the male, the duct of the mesonephros, and in the female, 

 as is well known, the whole of the Mullerian duct, forms the 

 adult genital duct (cf. Fig. 103). In the male the greater part 

 of the Mullerian duct degenerates or entirely disappears, thus losing 

 nearly all physiological significance. Its proximal vestige becomes 

 in Man the unstalked hydatid of Morgagni, a small appendage of 

 the testis ; its distal end, however, is believed to unite with that 

 of its fellow of the opposite side to form a vesicle, the " uterus 

 masculinus," which becomes embedded in the prostate, and later 

 opensTconjointly with the vasa deferentia, into the urinogenital 

 sinus (urethra). 1 



1 [The term "uterus masculinus" is applied, by analogy, to a somewhat 

 similarly placed median vesicle, opening into the prostatic portion of the urethra 

 in other Mammals. One well-known case is that of the common Rabbit. The 

 so-called " uterus masculinus " of that animal certainly does superficially resemble 

 that of Man, but the two differ fundamentally in their relationships to the vasa 

 differentia, i.e. in Man the bases of these pass behind the vesicle and open at its 

 sides, while in the Kabbit they pass in front of it and open within its anterior lip. 

 Kiilliker from the study of its development, has claimed for the so-called " uterus 

 masculinus" of the Rabbit) (fJiituncklungsf/csch. d. Menschen n. d. Mhern Thicre, 



