. Animal and vegetable physiology, considered with reference to natural theology. Biology; Physiology; Plant physiology; Natural theology. CHYLIFICATION. 149 i along the canal, so that it may receive tlie full action of these several agents, and yield the utmost (quantity of nutri- ment it is capable of affording. The total length of the intestinal tube differs much in dif- ferent animals, being in general, as already stated, smaller in the carnivorous tribes, than those which iced on substances of difficult dige stion, or affording but little nourishment. In these latter animals, the intestin
. Animal and vegetable physiology, considered with reference to natural theology. Biology; Physiology; Plant physiology; Natural theology. CHYLIFICATION. 149 i along the canal, so that it may receive tlie full action of these several agents, and yield the utmost (quantity of nutri- ment it is capable of affording. The total length of the intestinal tube differs much in dif- ferent animals, being in general, as already stated, smaller in the carnivorous tribes, than those which iced on substances of difficult dige stion, or affording but little nourishment. In these latter animals, the intestine is always of great length, exceeding that of the body many times; hence it is obliged to be folded into a spiral oi* serpentine course, forming many convolutions in the abdominal cavity. Sometimes, probably for greater convenience of package, instead of these nume- rous convolutions, a similai' effect of increasing the suri\ice of the inner membrane is obtained by raising it into a great number of folds, which project into tl>c cavity. These folds are often of consiflerable breadth, contributing not only to the extension of the surface foi' secretion and absorption, but also to the detention of the materials, with a view to their more complete elaboration. Remarkable examples of this kind of structure occur in most of the cartilaginous fishes, when the inner coat of the large in- testine is expanded into a broad fold, which, as is seen in fig. 316, representing this struc- ture in the interior of the intestine of the sliark, takes a spiral course; and this is con- tinued nearly the whole length of tlie canal, so that tlie internal surface is much augment- ed without any increase in the length of the intestine.* When the nature of the assimilatory pro- cess is such as to require the complete detention of the food, for a certain time, in particular situations, we find this ob- ject provided for by means of casca, or separate pouches • Structures of ttiis description have a
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