Page:Popular Science Monthly Volume 17.djvu/624

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be turned inside out without interference with the business of digestion. The skin in these cases must have a chemical digestive power,

PSM V17 D624 Sertularia pinnata.jpg
Fig. 6.—a, Sertularia (Diphasia) pinnata, natural size: a', fragment of the game enlarged, carrying a male capsule (a), and showing the hydrothecæ (h); b, fragment of Campanularia neglecta (after Hincks), showing the polypites contained in their hydrothecæ (h), and also the point at which the cœnosarc communicates with the stomach of the polypite (o).

as the food taken in mass, and frequently living substance, or even whole animals, is dissolved without trituration or mechanical aid.PSM V17 D624 Digestive system of a beetle.jpgFig. 7.—Digestive System of a Beetle (Carabus auratus): a, œsophagus; b, crop; c, gizzard; d, chylific stomach; e, Malpighian tubes; f, intestine; g, cloaca; h, supposed renal vessels. The human skin has powers of absorption, and in some slight degree a person may be fed through it. The continuation of the skin which lines the digestive canal is supplied with new powers of secretion; so that, instead of producing perspirations, oils, etc., it manufactures chemicals for changing food. Hence the principle of digestion and the character of the organs are fundamentally the same in all animals, the lowest with the highest. Only in the amoeba, hydra, etc., digestion is accomplished with the least possible expenditure.

A true stomach must be wholly devoted to the elaboration of food, leaving other functions to other organs. This requires that it be wholly shut off from other cavities of the body; and it were better to have two openings, one for reception of food, the other an outlet for waste matter, in order to give the food a single direction and prevent the mingling