There are some exceptions to the rule which we have just mentioned, res pecting the length of the canal in carni vorous and herbivorous animals. The seal, which takes animal food, has very long intestines ; the sea-otter resembles it in this respect, and differs therein most remarkably from the common otter, which resembles other carnivorous ani mals in the shortness of its intestinal tube. The length of canal in the former is twelve times that of the animal, and only three times and a quarter in the lat ter. (Home, in the Philos. Trans. 1799, part 2.) Whales have likewise a longer canal than other carnivorous mammalia; their stomach is complicated, and the in testine has longitudinal f dds. It seems, therefore, that a considerable length of intestinal canal is found in all mammalia which live much in the water, although they are carnivorous.
The plantigrade animals, which have carnivorous teeth, but feed equally well on vegetables, have a long canal ; but it is very narrow, and possesses no excum, nor distinction of large intestine.
A species of bat (vespertilio noctula) seems to have the shortest intestinal ca nal of any mammalia ; it is only twice the length of the animal's body. On the contrary, the rousette (vesp. vampyrus, Linn. v. caninus, Blum.) which lives en tirely on vegetables, has it seven times as long.
In a few instances, as the beaver and sloth, the rectum and urethra have a com mon termination, which may be compar ed to the cloaca of birds. This resem blance is the most striking in the orni thorhynchus.
A remarkable difference is observed in the length of the canal between the wild and domesticated breeds of the same species. In the wild boar the intes tines are to the body as nine to one ; in the tame animal these proportions are as thirteen to one. In the domestic cat, five to one ; in the wild cat, three to one ; in the bull, twenty-two to one ; in the buffalo, twelve to one. They are, on the contrary, longer in the wild than in the tame rabbit ; the proportions in the for mer being eleven, and in the latter nine to one.
The proportion of the intestinal canal to the length of the body, in birds, is as two, three, four, or five to one. It is not always longest and largest in the grami nivorous species, as many piscivorous birds have it equally long.
It is hardly twice the length of the body in many reptiles ; and not so much in the frog, although it is nine times as long as the space between the mouth and the anus in the tadpole.
The alimentary canal of some fishes is continued straight from the mouth to the antis, and does not, therefore, equal the length of the body. The lamprey, skate, and shark, are thus circumstanced.
Most birds have two cmca, which are longer in the galling: than in the carni vorous tribes. The rectum ends in a part called the cloaca, which is a large mem branous hag, containing also the termina tion of the ureters, that of the oviduct, the vasa deferentia, and of a membranous bag of unknown use, called bursa fabricii. This also holds the penis, where there is one.