Identifier: textbookofcompar00mill (find matches)
Title: A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine
Year: 1890 (1890s)
Authors: Mills, Wesley, 1847-1915
Subjects: Physiology, Comparative
Publisher: New York, London, D. Appleton and company
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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ionwhich is carried so far among the higher vertebrates. But, asrecent investigations have shown, such intra-cellular digestionexists to some extent in the alimentary canal of the highestmembers of the vertebrate group (see page 345). The means for grasping and triturating food among in-vertebrates are very complicated and varied, as are also thoseadapted for sucking the juices of prey. Examples to hand areto be found in the crab, crayfish, spider, grasshopper, beetle,etc., on the one hand, and the butterfly, housefly, leech, etc., onthe other. Before passing on to higher groups, it will be well to bearin mind that the digestive organs are to be regarded as the out-come both of heredity and adaptation to circumstances. Wefind parts of the intestine, e. g., retained in some animals inwhose economy they seem to serve little if any good purpose, as DIGESTION OF FOOD. 281 the vermiform appendix of man. Adaptation has been illus-trated in the lifetime of a single individual in a remarkable
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Fig. 228.—Diagram illustrating arrangement of intestine, nervous system, etc., in com-mon snail, Helix (after Huxley), m, mouth; t, tooth; od, odontophore; g, gullet;c, crop; a, stomach; r, rectum; a, anus; r. s, renal sac; h, heart; I, lung (modifiedpallia) chamber); n. its external aperture; em. thick edge of mantle united withsides of body; /, foot; cpg, cerebral, pedal, and parieto-splanchnic ganglia aggre-gated round gullet. manner ; thus, a seagull, by being fed on grain, has had itsstomach, naturally thin and soft-walled, converted into a mus-cular gizzard. Since digestion is a process in which the mechanical andchemical are both involved, and the food of animals differs sowidely, great variety in the alimentary tract, both anatomicaland physiological, must be expected. Vegetable food mustusually be eaten in much larger bulk to furnish the neededelements; hence the great length of intestine habitually foundin herbivorous animals, associated often with a capaciousand chambered

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