910 
The class Insecta is dicecious, and an intro- 
mittent organ is a common character throughout 
the entire race. In some insects, as in Aphis, 
the penis is double, and in the greater number 
it is associated with special organs, termed 
which assist in the impregnating act. 
greater number of molluscous animals are 
inhabitants of the deep, and amongst them 
considerable diversity, as respects mode of 
generation, exists. athe are hermaphrodite 
in organisation, and self impregnating ; others 
are hermaphrodite and mutually impregnating ; 
a considerable proportion are diccious, the 
male and female apparatus being on different 
individuals, and the impregnating fluid being 
conveyed by the medium in which they live 
from the male to the female animal; while 
some few are diecious and impregnate by 
mutual concurrence. The air-breathers, or 
Pulmonary Mollusca, are all hermaphrodite 
and impregnate by reciprocal coitus. e two 
last alone of the preceding modes of impregna- 
tion are those in which a true intromittent organ 
is required; hence, although rudiments of a 
nis may be discovered in many Mollusca, it 
is only in the mutually impregnating herma- 
phrodites and in the concurring diccia that it 
attains a size sufficiently bulky to render it an 
important character. Thus in the class Tuni- 
cata, which for the most part comprises self- 
impregnating hermaphrodites, no intromittent 
organ has been described. In the inhabitants 
of bivalve shells, which are either self-impreg- 
nating hermaphrodites, as the Oyster, or medi- 
ately impregnating diccia, as the fresh-water 
Mussel, Anodonta, there is no penis. The 
marine Gasteropoda are diccious; some, as 
the Patella, impregnating their females through 
the medium of the sea water by which they 
are surrounded, and others, including the whole 
of the Pectinibranchiata, impregnating imme- 
diately, being provided with a large penis for 
that purpose. In the genus Trochus the vas 
deferens terminates at the root of the penis, 
and the latter is grooved ; and in Carniaria the 
intromittent organ is bifid as well as grooved. 
In the Pulmonary Gasteropoda, as the snails 
and slugs, the generative organization is her- 
maphrodite, impregnation being reciprocal, and 
the penis of very large size. Among En- 
cephalous Mollusca, as in Pteropoda, the orga- 
nisation is also hermaphrodite, and the penis 
of large size. In Cephalopoda, the highest 
class of molluscous animals, the generative 
structure is diccious, but the penis is not 
intromittent. The penis in Sepia and Octapus 
is short and rudimentary, and pierced by a 
canal for the transmission of the seminal se- 
cretion ; but in the hooked Calamary the organ 
is simply grooved along its under part. 
In passing from the higher invertebrata to 
the class of Fishes we meet with a degradation 
of organization as regards the generative system. 
The penis, which we have seen to be properly 
formed for intromission in several of the inver- 
tebrate classes, is reduced to a mere papilla 
on the surface of the cloaca in fishes. In the 
Viviparous Blenny, however, in which internal 
impregnation takes place, the penis is larger in 
PENIS. 
size, and is probably increased in length duri 
coitus by eversion of the mucous lining of the 
vas deferens. In some of the higher — 
nous Fishes it is interesting to remark that 
rudimentary state of the penis is compensated 
for by the developement of an apparatus which __ 
seems intended to secure the contact of the 
cloace for an appreciable time. This apparatus 
consists of a pair of clasping organs, a provi- 
sion to which we have already had occasion to 
advert when speaking of the generative organs 
of insects. 
In Amphibia, as in Fishes, impregnation is — 
efiected by means of a close approximation, 
and in most instances by contact of the cloaca. 
There is no penis, but as a substitute for this 
organ the male animal is of an orga- — 
nisation fitted to maintain an embrace for a 
considerable period. 
The penis of the Ophidian group of 
is a true intromittent organ, and rema' 
the peculiarity of its structure. It consists of — 
two cecal processes, developed from the cloaca 
at its posterior part, and extending back into a 
cavity prolonged for a short distance towards 
the tail. These cceca are lined by a horny pa- 
pillated epithelium; they are invested wal 
moderately thick layer of erectile tissue, and 
have oof muscles attached to their extre- 
mity. When the animal is excited by the vene- 
real orgasm the turgescence of the erectile tissue 
causes the eversion of the ceca and their pro- 
trusion through the aperture of the clo 
Restored to the state of repose, ey oo, e 
tracted by their muscles, and drawn into. 
their original position. In the Rattlesnake a 
singular modification of the intromittent orga 
occurs, in the bifid termination of each of 
ceca. We cannot view the peculiarity of strue- 
ture exhibited by Ophidia, without recalling t 
mind the similarly inverted disposition of the 
intromittent organ, which we have already seer 
among the Invertebrata, namely, in Arachnida 
The Lacertine Sauria are possessed of an in 
verted intromittent organ, similar to that o 
Ophidia. In the Crocodile, however, the penis 
is no longer an inverted cecal pouch; it | 
grooved along its under part, attached by tw 
crura to the pubic bones, and furnished with 
rudimentary glans at its extremity. But ev 
in the Crocodile there exists a peculiari 
structure which allies the family with the ] 
tine Sauria and Ophidia. The structure 
which I allude, is a canal which is pre 
from the peritoneal cavity for a short dista 
into the substance of the penis, and 
minates by a cecal extremity. ¥ 
In Chelonia, the same kind of intromit 
organ occurs as is found in Crocodiles,a groa 
penis contained within the vestibule of 
cloaca, attached to the pubic bones, ai 
lowed by one or more peritoneal canals. 
iles 
pak 
it 
a 
important difference, however, is met with 
we compare the two groups of Chelonia, 
marine and the land tortoises. In the form 
scarcely any obstruction to impregnation res 
from the covering of the animal; the penis 
consequently small. But in the land torto 
where the shell extends beyond the limit 
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