XV REPRODUCTIVE ORGANS 407 
versa? ‘To this question no decisive answer can at present be 
given. 
The terminal relations of the kidney-ducts and the gonoducts, 
and the presence of accessory or of vestigial organs in connexion 
with them, will now be briefly dealt with. In the males of the 
Elasmobranchs the mesonephric ducts which, as already pointed 
out, act both as kidney-ducts and gonoducts, dilate posteriorly 
to form a pair of vesiculae seminales, and then unite to form 
a urinogenital sinus, opening into the cloaca at the extremity 
of a median papilla (Fig. 250, C). The sinus also receives ducts 
from the hinder part of the mesonephros, either separately, as in 
the female, or by a common duct on each side—the so-called 
metanephric duct—as in the male. Two tubular caecal out- 
growths from the sinus form two sperm sacs. Only the anterior 
portions of the Miillerian ducts with their coelomic apertures are 
retained in the adult. In the female the mesonephric ducts are 
purely excretory, but otherwise they are similar, and the oviducts 
(Miillerian ducts) open into the cloaca separately or by a 
common orifice (Fig. 230, D). A glandular dilatation of each 
oviduct forms the oviducal or shell gland by which the horny 
ego-cases are secreted. In the males of the Holocephali the 
gonoducts open into a urinogenital sinus with an external orifice 
distinct from and behind the anus; but the female has separate 
apertures for the rectum, the conjoined oviducts, and the 
united mesonephric ducts. Both sexes have complete Miillerian 
ducts communicating with the coelom in front, and behind with 
the exterior. The Dipnoi of both sexes essentially resemble 
the Elasmobranchs in the general relations of their ducts, but the 
Miillerian ducts of the male exhibit marked differences in the 
three genera.’ In Neoceratodus the ducts are as complete as their 
functional representatives in the female. Protopterus retains 
anterior vestiges and the coelomic apertures, and also vestiges of the 
hinder portions which unite and end blindly in the urinogenital 
papilla, but the middle sections of the two ducts are suppressed 
(Fig. 233, B). In the Teleostomi there is a general similarity 
in the terminal relations of the gonoducts and kidney-ducts. In 
the Ganoids the archinephric ducts unite and then expand into 
a urinary sinus or bladder, and the gonoducts of the female, or 
of both sexes in Lepidosteus, open either into the archinephric 
1 Graham Kerr, op. cit. 
