1006 
sents itself under three principal types, each of 
which will merit distinct considération. 
The first is that observed in the Dermapte- 
Pye ve or Cyclostomatous Fishes, such as 
the Myxine and Lamprey ; but it is not pe- 
culiar to this group, seeing that the Eels and 
perhaps other races have a similar organi- 
zation. 
On opening the abdomen of one of these 
Fishes, as, for example, the Lamprey, ( Pe- 
tromyzon marinus, fig. 534) an exceedingly 
S 
' Female generative organs of the Lamprey 
( Petromyzon marinus). 
a, parietes of abdomen; 5b, cavity of ditto; 
c, Ovary; e, external pesenge leading into abdo- 
minal cavity, through which the ova are discharged; 
g, kidney. 
extensive membranous expansion is found sus- 
ended in loose folds, which is attached by a 
ind of mesentery beneath the spinal column, 
and extending along the whole length of the 
abdominal cavity. Except in the breeding 
Fig. 535. 
One of the folds of the ovary of the Lamprey, 
( Petromyzon marinus, ) showing t losed ova. 
PISCES. 
season, this membrane, of which a portion only 
is represented in the figure, (fig. 534, c,) is 
thin and transparent, but at the same time 
exhibits considerable vascularity. When the 
breeding season approaches, innumerable gra- 
nules begin to 5 their appearance, between 
the two layers of which this expansion consists, 
which in the female soon proclaim themselves to 
be ova (fig. 535), and, as they increase in size, 
gradually distend the whole abdomen. On 
opening the fish in this condition the abdominal 
cavity appears to be completely filled with 
innumerable ova beautifully arranged in rich 
festoons, all of which are connected in front 
of the spinal column. When the ova are 
quite mature they are cast loose from the ovary 
and escape from the ovarian membrane in 
which they were formed, into the general ca- 
vity of the abdomen, wherein they may be 
found at this period floating quite loose prepa- 
ratory to their expulsion. This is ultimately 
effected through a simple but wide orifice (e) 
situated immediately behind the anal aperture, 
and causing a free communication to exist be- 
tween the peritoneal cavity and the exterior of 
the body, so that the ova easily pass out and 
are ejected into the surrounding water. ig 
In the males of those Fishes which offer this 
type of the generative system the appearance 
of the reproductive organ is, while in a state of 
inactivity, so exactly similar to that of the 
female as to preclude the possibility of distin- 
guishing the two from each other; but, as the 
breeding season advances, the difference be- 
comes apparent; the festooned membrane, 
which must in this case be called the testis, 
secretes a kind of milt or seminal fluid, rich in 
seminal animalcules, which in the same manner 
as the ova of the female escapes into the peri- 
toneal cavity and is expelled through a post-— 
anal orifice to be diffused through the sur- 
rounding water, by the agency of which it is 
applied to the previously deposited spawn of 
the female, whose ova thus ming vivified 
are left to the mercy of circumstances to be 
destroyed or hatched in due season. 
In the second form of the generative app 
ratus which is common to almost all the tru 
osseous Fishes, a very different arrangement 
met with. The folds of the ovarian membrar 
instead of being loosely suspended in the abe 
minal cavity, are now completely enclosed 
two capacious membranous capsules, situa 
one on each side of the spine, and which 
distended with ova occupy a very large share 
the abdomen. On opening one of these cap 
sules, the ova which it contains are seen, how- 
ever, to be developed between the two layers ¢ 
the proper ovary, exactly as in the case of 
Lamprey, and to be attached in broad festoons 
to the interior of its walls, the essential diffe. 
rence being that whereas in the preceding typé 
the eggs, when expelled from the ovary, ese 
into the peritoneal sac, they now are retained by 
the capsular envelope of the ovary, whence they 
are expelled through excretory canals provic 
for the purpose. These, as they exist in t 
Herring, are represented in the annexed figu 
(fig. 536); from the posterior extremity of ez 
