848 
ZOOLOGY. 
internal view of the belly of the viviparous dog-fish, squa- 
lus acanthius of Linnaeus, to shew the appearance of the 
stomach and intestine in situ, and their relative situation 
to the other viscera: a, the heart; b b, the liver; the 
left lobe is cut away to expose the parts behind; c, the 
oesophagus; d, the cardiac portion of the stomach; e, the 
pyloric portion ; f, the small cavity between the pylorus and 
duodenum; g, the duodenum; h h, the valvular intestine; 
i i, an appendix, with which it communicates; k k, the 
testicle; 11, the vas deferens, the lower portion of which is 
straight, and distended with semen ; m, the cavity which is 
the reservoir of semen, and urinary bladder; n, the kidney ; 
o, the penis; p p, two external openings leading into the 
cavity of the abdomen ; q q, the two holders, in their col¬ 
lapsed state. f 
Fig. 26*. A male burbot, (gadus lota) laid open, in 
order to shew the position of the various viscera : the bran¬ 
chial membrane also, (c). is stretched, in order to display the 
gills; a, the heart; d, the abdominal fin ; e, the pectoral 
fin ; f the inferior layer of the pericardium; g, the liver; 
h, the testicles; i, the spleen ; k, the intestine; l, the 
rectum; m, the bladder; n, the anus ; o, the anal fin. 
Fig. 19 and 20, specimens of the internal parts in situ 
in the amphibia: 19, being a dissection of a female frog; 20, 
the interior of a fecundated female frog. 
19. a, A pin that holds up the retroverted heart of the frog; 
b, the heart; c c, the fimbriated extremities of the oviducts; 
d d, sinuosities of the oviducts, and e, blood-vessels of the 
fimbriae; f the opening of these ducts into the two enlarged 
cavities, gg, analogous to the uterus of higher animals; they 
terminate in the rectum, h, wherein also the double urinary 
bladder opens at i. 
The same figure represents the ovary of one side, k; it is 
contracted, and far removed from the fimbriae of the oviducts; 
/, one of the kidneys; m, the fatty appendices of the 
ovaries; n n, two small ova, floating in the cavity of the 
abdomen ; o, an ovum in the oviduct. 
p, shews the stomach and small intestines; q, part of the 
liver; r, the gall bladder; s s, the lungs and pulmonary 
vessels, one lung being partly removed, the other distended 
with air ; 11, the auricle of the heart, (internally divided by 
a valve); u u, the cut edges of the integuments of the chest 
and abdomen. 
Fig. 20. The ova in the ovaries: a, ova dispersed through 
the abdomen ; b, c, some near the fimbriae; d, e,some within 
the oviduct; f, some entering the uterine portion of the duct; 
g, one side of this uterine portion in its natural state, trans¬ 
parent, and therefore discovering its contained eggs; h, the 
opposite side opened, to display these completely; i, the single 
opening of both the false uteri. In the upper part of the 
figure are seen the heart and aorta: k k, the two branches 
this gives off; l /, the orifices of the oviducts; in m, the 
lungs. 
Fig 7 denotes the ovaries of the louse : a, two flat bo¬ 
dies that project beyond the vulva; b b b. the extremities 
of the oviducts, united on one side as they always are, until 
separated by the dissector; c, the oviduct with perfect eggs d, 
or such as are incipient, e e; f the two mam branches of 
the oviducts; g g, the five subdivisions of each; h, indicates 
what Swammerdam calls the uterus, containing an ovum; 
i k, a sac that pours a glutinous secretion upon the ovum; 
l, a contracted part of the uterus. 
Fig. 9 marks the ovaries of the snail: r, the ova inflated. 
Of the locomotive system in vermes and insectas.—In the 
mollusca, the first trace of a skeleton is in the ssepise, where 
it forms a cartilaginous ring, closely connected with the 
nervous circle of the neck. 
In some testacea the body is enclosed in a solid calcareous 
tube, with the addition of some detached portions serving to 
bore into wood, as in the teredines. In other instances the 
number of portions of calcareous shell is multiplied, as in the 
balani, where they are six. Lastly, the form of the bivalve 
shells undergoes a variety of modifications, the two pieces 
being sometimes similar, at others altogether unlike, as in 
the oyster; or completely incorporated, as in the pinnae. 
As for the efficient apparatus for motion, the muscles, the 
most remarkable organ belonging to it is a fibrous mem¬ 
brane, which commonly surrounds the whole of the body, 
and is called generally the cloak. 
The opening of the shells in bivalves is effected by a 
fibrous ligament at the hinge; as an antagonist to which 
there is usually a strong short muscle at the anterior and pos¬ 
terior extremities of the shells, attached to both of them, and 
serving to bring them together: such is the case in Venus 
my a, unio, solen, and many other genera. In others of the 
bivalves, however, as ostrea, spondylus, &c., there is but 
one muscle of this kind. In the next place we have to con¬ 
sider the foot, as it is called, serving not only as an organ 
of locomotion, but also for many other purposes: it is a 
fleshy mass, which contains the intestine, liver, and ovary, 
is attached by muscles of its own to the shell, and in some 
genera, as cardium and mytilus, is considerably elongated 
and apparently highly organized. In the fresh-water muscle, 
the foot, when employed in creeping along the ground like 
a snail, and stretched to its lull length, is as long as the entire 
animal, though scarcely half its size when retracted; it is 
covered on each side with a double layer of decussating 
muscular fibres, which terminate posteriorly in two long, 
and anieriorly in two short tendons attached to the shell; its 
basis, also, presents many transverse fibres. In other genera, 
the structure of the foot varies in a greater or less degree from 
that here described ; the most important circumstance, how¬ 
ever, to he remarked, is, that the excretory duct of a gland 
opens on its base in several genera (mytilus, pinna, avi- 
cjula, &c.) and pours out a tenacious mucus, which the ani¬ 
mal draws into-threads by the tongue-like point of the foot, 
and in that manner attaches itself to the rocks. 
Of the active organs of motion in snails, slugs, &c., with¬ 
out shells, the most important is an external muscular mem¬ 
brane, (panniculus carnosus) in which the viscera are con¬ 
tained as in a bag. Strong fibres decussating in every direc¬ 
tion, are found on this covering, and particularly on its 
broad abdominal surface. The name of foot is applied to 
that part on which the animal crawls. Mucus is copiously 
secreted from the under surface of this part, by which means 
the animal attaches itself, as well as by the vacuum pro¬ 
duced by fixing its edges, and then retracting the space in¬ 
cluded within them. 
We have, in fig. 46, an example of the locomotive sys¬ 
tem in an helix, where q marks the foot; a marks the spiral 
portion of the shell, into which the majority of the muscles 
are inserted; b b, muscles of the foot; c, of the tail, or 
hinder part of the foot; d( the point to which the anterior 
muscles are attached; e, the small muscle which retracts the 
mouth, throat, and tongue g, which is armed with teeth,y- 
d d, the muscles that retract the eyes and larger horns, kk$ 
(z i, the optic nerves are seen across them ;) / /, small mus¬ 
cles that retract the lips; m m, retractors of the lesser horns; 
n n, very strong muscles inserted into the middle of the 
body, and compressing it. 
The principal organ of motion, in the articulated worms, 
is a fibrous muscular membrane, inclosing the viscera, and 
placed immediately beneath the externa! mucous covering. 
In it we particularly distinguish four bundles of longitudinal 
fibres; two of which are placed on the belly, and two on 
the hack; and by the alternate or simultaneous contractions 
of which the various motions of the body are effected. 
When bristles or tufts of hair supply the place of feet in lo¬ 
comotion, they are set in action by peculiar fibres, which 
enable the animal to regulate their protrusion and retraction 
at pleasure. Where these are wanting, and where the pro¬ 
gression of the animal is accomplished by fixing the extre¬ 
mities alternately, we find either moveable hooks, as in seve¬ 
ral of the intestinal worms, or else two suckers situated 
at each extremity of the body. In the order crustaceae, we 
find that the articulation of the body, as it exists in insects, 
becomes more evident; new organs of motion—feet, being 
also developed at the rings or joints of the body. 
Locomotion in the Crustacea is performed by tolerably 
firm muscles, which present this peculiarity in their disposi¬ 
tion 
