It has already been shown by the illustration, (p. 4,) that the paunch is the largest of the four cavities; but this is not the case with the stomach of the young calf, which, while it continues to suck, does not ruminate; in this case the _reed_, which is the true digestive cavity, is actually larger than the other three taken together. When the calf begins to feed upon solid food, then it begins to ruminate; and as the quantity of solid food is increased, so does the size of the paunch increase, until it attains its full dimensions. In this latter case, the _paunch_ has become considerably larger than the other three cavities taken together. A curious modification of an organ to adjust itself to the altered condition of the animal is beautifully shown in the instance now under consideration, the nature of which will be easily understood by a reference to the following diagrams, giving the exact relative proportions of the different cavities of the stomach to each other in the young calf and in the full-grown cow. [I am informed by Professor Symonds, of the Royal Veterinary College, that the two following sketches should be placed in the page so as to be viewed with the oesophagus to the right, and the pylorus to the left, instead of being, as they now are, at the top and the bottom; but as the present object is only to show the relative sizes of the different cavities, the error is not of much consequence.] The letters refer to the same parts in each figure: _a_, the paunch; _b_, the honeycomb bag; _c_, the many-plies; _d_, the reed. [Illustration: Outline of the Stomach of a Calf about a fortnight old.] [Illustration: Outline of the Stomach of a full-grown Cow.] [These engravings, illustrative of the comparative sizes of the different stomachal cavities, are copied from original drawings taken from preparations of the stomachs which I made expressly for this purpose.] In all herbivorous animals, and especially those of the ruminating kind, the alimentary canal is of an enormous length; measuring in a full grown ox, as much as sixty yards. The paunch, in such an animal, will hold from fifteen to eighteen gallons. Blumenbach observes, that the process of rumination supposes a power of voluntary motion in the oesophagus; and, indeed, the influence of the will throughout the whole process is incontestible. It is not confined to any particular time, since the animal can delay it according to circumstances, even when the paunch is quite full. It has been expressly stated of some men, who have had the power of ruminating, that it was quite voluntary with them. Blumenbach knew four men who ruminated their food, and they assured him they had a real enjoyment in doing it: two of them had the power of doing or abstaining from it at their pleasure.