ELASMOBRANCIIS. 
1077 
in the skin of the ventral side, between the anus and 
the urethral aperture, are equally tumid during the 
breeding-season, it seems highly probable that both the 
pterygopodia functionate simultaneously. The situation 
of the urogenital opening in the males, relatively to 
the base of the pterygopodia, is such that the semen 
may apparently be received almost immediately in the 
above-mentioned channel on the pterygopodia. 
The ovaries (fig. 303, n) occupy the same position 
as the testes — in the anterior part of the abdominal 
cavity they are attached by means of their mesoarium 
(peritoneal fold) to the spinal column — but are sepa- 
rated from their efferent (the Mullerian) ducts, which 
unite before them, under the oesophagus and just be- 
hind the diaphragm, in a curve, at the middle of which 
they have their common opening (</). To this opening 
the eggs thrown off by the ovaries are conducted by 
a, current produced by the ciliary motion of the investing 
cells of the serous tissue lining the interjacent organs. 
The said current may be observed even shortly after 
the death of the fish by opening the belly, removing 
or lifting aside the liver, and strewing finely powdered 
charcoal on the parts. The oviducts (Mullerian ducts) 
bend backwards, one on each side, and are each fur- 
nished with two dilatations. The anterior (a) of these 
is glandular, its walls being traversed by ramified ducts 
that secrete a nidamental substance to envelop the eggs; 
while the posterior (r) is a uterine pouch within which 
the impregnated ova either undergo the earliest stages 
of their development, or remain until the young are 
fully developed and capable of free motion. In the 
latter case, when only the right ovary as a rule is 
functional, the glandular dilatation of the oviducts is 
little developed, but the uterus all the more so, its 
walls being lined with vascular folds or even with a 
placenta uterina, into which the vitelline sac of the 
embryo is fitted by means of warty placental growths 
(cotyledons), an arrangement that would be fully ana- 
logous to the viviparous development of the mammals, 
if the yolk sac were replaced by the foetal membranes 
of the latter. The oviducts open either into the com- 
mon cloaca (.s, .s), on each side of the urethral aper- 
ture ( t ), or, as mentioned above, at special orifices in 
the skin. 
The primeval type of the Elasmobranchs has rami- 
fied in two essentially different directions of evolution, 
on the one hand to the Holocephali, on the other to 
the Plagiostomi. 
Fig. 303. Female organs of a Shark. After Owen. 
a, ventral wall, cut open and laid back; b , sections of the shoulder- 
girdle and pelvis; c, heart in its pericardium; h, hindmost part of 
the rectum and the ascending glandula retroanalis; n, right ovary; 
o, nidamental dilatation of the left oviduct ( glandula nidamental is); 
q , common aperture of the two oviducts; at its bottom the orifice of 
the right oviduct (to the left in the figure); r, uterine division of 
the left oviduct (the right oviduct lies unopened to the left of the 
figure); s, posterior mouths of the two oviducts; t, urethral papilla, 
at the tip of which a bristle is inserted into the urethra. On each 
side of Ibis bristle may be seen an abdominal pore (the mouth of a 
peritoneal canal). 
