COMPARATIVE ANATOMY. 
ed by an exterior crust of cortical sub- 
stance. This is the ease in all the ferae, 
and in 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 fretjuent the water. I have ob- 
served it in the seal and porpoise, where 
the small kidneys are extremely numerous, 
and send branches to the ureter without 
forming a pelvis. Mr. Hunter states that 
it belongs to all the whales. (“ Philos. 
Transact. 1807, pt. 2.”) The otter has 
the same structure; but its small kidneys 
are not so numerous as in the animals 
above-mentioned. (“ Home, of the sea-ot- 
ter, (lutra marina), Philos. Trans. 1796, 
pt. 2.”) It is remarkable that the brown 
bear (ursus arctos), which lives on land, 
should have 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. Mr. Hunter concludes, that 
it is because nature wishes to preserve an 
uniformity in the structure of similar ani- 
mals. But the badger, (ursus meles), which 
is a very similar animal, has the uni lobular 
kidney. The munber of small kidneys in 
the bear is 50 or 60, and it appears that 
each consists of two papillae. 
The kidneys of birds form a double row 
of distinct, but connected glandular bodies, 
placed on both sides of the lumbar verte- 
brae, in cavities of tlie ossa innomiiiata. 
The urinary bladder does not exist in this 
whole class, and the ureters open into the 
cloaca. 
Animals of the genus testudo and raiia 
have a large bladder in the situation of the 
urinary receptacle of other animals. This 
is double in many of the frogs properly so 
called. These bags are represented both 
by Blumenbach and Cuvier as urinary blad- 
ders ; but Townson has already shewn, that 
in the frog and toad they have no connec- 
tion with the ureters, which open at the 
back of the rectum, while those receptacles 
terminate on the front of the intestine. 
(“Tracts and Observations,” p. 66. tig. 3). 
The writer of this article has observed the 
same structure in a male and female tor- 
toise. 
ORGANS OF GENERATION. 
The nature of generation, which is the 
greatest mystery in the economy of living 
bodies, is st'dl involved in impenetrable ob- 
scurity. The creation of a living body, that 
is, its formation by tlie union of particles 
suddenly brought together, has not hitherto 
been proved by any direct observation. 
The eomparison of tlris process to that of 
crystallization is founded in a false analogy : 
crystals are formed of similar particles at- 
tracting each other indifferently, and agglu- 
tinated by their surfaces, which determiue 
the order of their arrangement : living bo- 
dies, on tlie contrary, consist of numerous 
fibres or laminae of heterogeneous composi- 
tion, and various figures, each of which has 
its peculiar situation in relation to the other 
fibres and lamina;. Moreover, from the in- 
stant in which a living body can be said to 
exist, however small it may be, it possesses 
all its parts; it does not grow by the addi- 
tion of any new laminae, but by the uniform 
or irregular developement of parts which 
existed before any sensible growth. 
The only circumstance common to all 
generation, and consequently, the only es- 
sential part of the process, is, tliat every 
living body is attached at first to a larger 
body of the same species with itself. It-con- 
stitutes a part of this larger body, and de- 
rives nourishment for a certain time from 
its juices. The subsequent separation con- 
stitutes birth ; and may be the simple re- 
sult of the life of the larger body, and of 
the consequent developement of the smaller, 
witliout the addition of any occasional ac- 
tion. 
Thus the essence of generation consists 
in the appearance of a small orgaTiised body 
in or upon some part of a larger one ; from 
which it is separated at a certain period in 
order, to assume an independent existence. 
All the processes and organs, which 
co-operate in.the business of generation in 
certain classes, are only accessory to this 
primary function. 
AVhen the function is thus reduced to 
its most simple state, it constitutes the gem- 
miparous, or generation by shoots. In thw 
way the buds of trees are developed into 
branches, from which other trees may be 
formed. The polypes (hydra) and the sea- 
anemones (actinia) multiply in this manner ; 
some worms are propagated by a division 
of their body, and must therefore be ar- 
ranged in the same division. This mode of 
generation requires no distinction of sex, 
no copulation, nor any particular organ. 
Other modes of generation are accom- 
plished in appropriate organs : the germs 
appear in a definite situation in the body, 
and tlie assistance of certain operations is 
