ZOOLOGY. 
this heart, but its dilatation is effected by a multitude of mus¬ 
cles, which at first sight appear as one, but may by care be 
divided. 
Fig. 17. The arterial system of the frog. 
Fig. 18. The venous system of the frog. 
Fig. 17. a, The ventricle; b, the auricle. The aorta is seen 
issuing from the ventricle, and dividing into two branches; 
con the right, and d on the left sides. These vessels divide 
into three chief branches, the first of which, eee, goes to the 
substance of the lungs in part, and partly to the air cells, 
around which it forms anastomoses with the pulmonary 
vein. Its divisions are represented as divided ; these pulmo¬ 
nary arteries send off two recurrent branches, ff, to the 
mouth. 
The second pair of branches are represented at gg, where 
they form a considerable dilatation, of a dark grey colour; 
these arteries form a similar dilatation a little higher, and are 
distributed to the respiratory muscles of the mouth and chest. 
The third pair of principal branches of the main artery 
are considerable. These branches form the trunk of the 
lumbar aorta, by uniting together. Each arising from the great 
trunk near the heart, forms a curve near the lungs, h h ; they 
give off, 1, the axillary, i i, which arise from their outer side; 
2, the carotid, k k, which run up to the head, and penetrate 
its bones; 3, the vertebral, which unites with its fellow by 
an extensive anastomosis, from which the common trunk of 
thecoeliac and inferior mesenteric is derived ; 4, many small 
arteries, as the lumbar, n n; those going to the testicles; to the 
ovaries, oo; to the kidneys, p, &c. Finally the trunk divides 
into two iliacs. 
Fig. 18. The distribution of the veins is very different 
from that of the arteries. The two trunks of the vena cava, 
a a, which arise from the upper part of the auricle, where the 
two arterial trunks that are cut off, are situate, send off two 
pulmonary veins, c c, also cut off, that are double the size of 
the corresponding arteries, and are distributed to the pul¬ 
monary cells. The two superior trunks of the vena cava 
superior, are situate upon the corresponding arteries, and, like 
them, divide into several branches, of which some, dd, are 
distributed to the different parts of the mouth ; others, e e, 
turn upwards to the head, distributing a few branches, ff, 
to the fore-legs; the axillary veins, gg, which chiefly belong 
to the fore-legs, send two remarkable branches, h h, to the 
iliac region, where they are distributed between the muscles 
and the skin. The inferior vena cava, i i, that arises from 
the apex of the heart, divides into three branches, which are 
distributed to the liver, k k ; a little below, the mesenteric 
vein, l, emerges from the liver; rn, indicates the renal veins; 
n, the iliac; o, the epigastric. 
The fig. 25 shews the respiratory system in the butterfly. 
The tracheae, a a, lie among the ovaries and the fat. 
At fig. 11 is represented the interior of the chrysalis of the 
bee: a a, indicate the stomach perforated by numerous tra¬ 
cheae, and covered by muscular fibres, marked ec; b b, the 
oesophagus; c c, glandulous bodies; g, four intestinal cceca, 
terminating below the pylorus, /,-at h h-, i shews the re¬ 
maining portion of the intestine, to the extremity whereof 
the sting is represented adhering. The shadowed parts of the 
figure marked /, shew the appearance the coagulated food in 
the stomach presents through its parietes. 
Some difference between the pulmonary systems of the 
preceding insect and the bee, will be observed by referring 
to fig. 24. In the latter the ramifications of the tracheae 
dilate into two large bags, a a, whence other ramifications pass 
out, b b, which terminate in other vesicles, c c, which again 
send forth branches, d d, and, by the continuance of this 
arrangement, the air is carried by vessels, e e, to all parts of 
the body. 
In the scarabreus nasicornis, it will be noticed, that while 
a worm, this animal has merely as tracheae, minute vessels 
carrying air, but that afterwards these are swelled out into 
vesicles, or air cells. These are readily distinguished by a 
reference to fig. 23. They are hollow cylinders somewhat 
leaf-shaped, of a white colour and flocculent appearance. 
Voju XXIV. No, 1677. 
841 
The tracheae leading to them have, on the other hand, the 
shining appearance of mother of pearl. 
Fig. 8 shews the circulating and respiratory systems of the 
ephemera; o o, mark the tracheae; tt, the heart; ss, a sort 
of pen lying beneath the tracheae; mi, the tracheae cut 
off; xx x, enlargements taking place in different parts of the 
heart. 
Urinary organs are absent in the vermes and insecta.— 
“Although,” as Blumenbach observes, “we cannot perceive 
of what use an urinary bladder can be to fishes, and animals 
which live in water, several genera and specie, have one.” 
These are the two large bags which Blumenbach and Cuvier 
represent as urinary bladders of the frog and toad, but are 
stated by Townson to have no connexion with the ureter. 
Indeed it is very clear that the ureters open at the posterior 
part of the rectum, while these two receptacles terminate on 
the front of that intestine. He states that the fluid contained 
in these reservoirs is a pure water. The size of these bags, 
which exceeds all ordinary proportion to the bulk of the 
kidney, renders it likewise probable that they are not recep¬ 
tacles of urine. Either of the bags is at least twenty or 
thirty times as large as the kidney. The testudo has a 
bladder. 
The kidneys of birds (with a few exceptions, as the cor¬ 
morant, &c.) form a double row of distinct but connected 
glandular bodies, placed on both sides of the lumbar verte 
bra, in cavities of the ossa innominata; one of the most in¬ 
structive examples of the remarkable analogy between the 
structure of the secreting viscera, properly so called, and the 
conglomerate glands. The urinary bladder is wanting in the 
whole class, and the ureters open into the cloaca. 
The structure of the kidney in mammalia displays two 
very opposite varieties, which may be called the simple and 
the conglomerate kidneys. In the former there is a single 
papilla, which is surrounded by an exterior crust of the cor¬ 
tical substance. This is the case in all the ferae; and in some 
other animals, as many rodentia. The other kind of kidney 
consists of an aggregation of small kidneys, connected by 
cellular substance. It appears that this form of the gland is 
found in all those mammalia which either live in, or frequent 
the water. Thus in the seal and porpoise the small kidneys 
are extremely numerous, and send branches to the ureter 
without forming a pelvis. Mr. Hunter states that this struc¬ 
ture belongs to all the whales. The otter has the same struc¬ 
ture; but its small kidneys are not so numerous as in the 
animals above-mentioned. The brown bear, (ursus arctos) 
however, which lives on land, has this structure as well as the 
white polar bear, (ursus maritimus) which inhabiting the 
coasts and floating ice of the northern regions, spends much 
of its time in the water. But the badger, (ursus meles) which 
is a very similar animal, has the uni-lobular kidney. The 
number of small kidneys in the bear is 50 or 60; and it 
appears that each consists of two papillae. The suprarenal 
glands, (glandulae suprarenales) as their name implies, are 
intimately connected with the kidneys; but their functions, 
as well as those of the thyroid and thoracic glands, still re¬ 
main unknown. They appear, from the latest anatomical 
researches, to have a great sympathy with the sexual organs. 
The urinary bladder is more loose in the abdomen of most 
quadrupeds than in the human subject. It is comparatively 
much smaller in carnivorous than in herbivorous animals; 
and is particularly large in the ruminating bisulca and the 
hare. 
The external covering of the body is, in a great number of 
vermes, a mere organ of defence; in many others it is the 
grand organ of imbibition and respiration. In insects it 
performs the offices of defence, and, by means of the trachea, 
that open upon it, of respiration. The epidermis is very early 
seen as a distinct membrane. 
In the testacea it usually covers the surface of the shell, 
and obscures the brilliancy of that part until it is removed. 
It may be seen by plunging a snail-shell into boiling water. 
It is very thick and villous in some species, as in the area 
pilosa. 
9 C 
Crustacea 
