URINARY ORGANS.
The structure of the kidney in the mammalia displays two very opposite varieties, which may be called the simple and the conglomerated kidneys. In the former there is a single papilla, which is surrounded by an exterior crust of cortical substance. This is the case in all the ferx, and in many rodentia. The other kind of kidney consists of an ag gregation 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 fre. quent the water. I have observed 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. (" Phi los. Transact. 1807, pt. 2.") The otter has the same structure ; but its small kid neys are not so numerous as in the ani mals above-mentioned. (" Home, of the sea-otter (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 smariti mus,) 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 animals. But the badger, (ursus meles,) which is a very similar animal, has the uni-lobu lar kidney. The number of small kidneys in the bear is 50 or 60, and it appears that each consists of two pa The kidneys of birds form a double row of distinct, but connected glandular bodies, placed on both sides of the lum bar vertebra, in cavities of the ossa in nominata. The urinary bladder does not exist in this whole class, and the ureters open into cloaca.
Animals of the genus testudo and rana have a large bladder in the situation of the urinary receptacle of other animals. This is double in many of the frogs, pro perly so called. These bags are repre sented both by Blumenbach and Cuvicr as urinary bladders ; but Townson has already shown, that in the frog and toad they have no connection with the ure ters, which open at the back of the rectum, while those receptacles termi nate on the front of the intestine. (" Tracts and Observations," p. 66. fig. 3.) The writer of this article has ob served the same structure in a male and female tortoise.