404 FISHES CHAP. 
The nature and homologies of the genital ducts in the 
different groups of Fishes are amongst the most puzzling of the 
many problems which vex the soul of the Vertebrate morpho- 
logist, and although there is a fairly general agreement on some 
points, there are others of great importance of which it may be 
said quot homines, tot sententiae. 
Broadly speaking, there are two types of genital ducts in 
Fishes: (1) those which are obviously derived from some part 
of the kidney system; and (2) those which are special ducts and 
appear to have no connexion with kidney-ducts. 
The Elasmobranchs offer a typical example of gonoducts of 
the first kind. At an early embryonic period in both sexes 
each archinephric duct becomes longitudinally split into two 
ducts, of which one continues to receive the openings of the 
mesonephric tubules and remains as a mesonephric duct (Fig. 
229, B).' The other, which has no connexion with the meso- 
nephros, opens anteriorly into the coelom by means of the 
united nephrostomes of the pronephros, and is known as the 
“Miillerian duct” (Fig. 230, C and D). In the adult male 
the Miillerian ducts are useless vestiges, but in the female they 
persist and act as oviducts, receiving the eggs set free from 
the ovarian ovisacs through their coelomic apertures, and thence 
conveying them to the cloaca. In the male, certain of the 
anterior mesonephric tubules become connected with the testi- 
cular ampullae by means of a network of slender tubules, the 
“vasa efferentia ” or testicular network, and through the latter the 
spermatozoa pass from the testes to the mesonephric duct (Fig. 
230, C). Consequently, the mesonephric duct conveys both 
spermatozoa and the kidney excretion to the cloaca. It is 
obvious, therefore, that both the male and female gonoducts are 
derived from kidney-ducts. 
The Teleostei afford an equally typical illustration of the 
second type. Each female gonoduct (oviduct) is formed by a 
backward growth of the same two peritoneal folds which enclose 
the ovary; these are converted into a “peritoneal tube” or 
canal by the union of their margins. The male gonoducts 
are also formed in continuity with the testes, that is, as 
backward prolongations from the latter. Each duct, male or 
1 Semper, Centralblatt f. Med. Wiss. 1875, No. 29; F. M. Balfour, Jowrn. Anat. 
and Phys. x. 1875, p. 17; Id. Comparative Embryology, London, 1881, ii. p. 568. 
