STOMACH. The anatomy and physiology of the human stomach is treated in the article DwEgriox, ante. This organ, the most important for the preparation of the nutriment of the body. varies greatly in different animals. Some of the protozoa, as infusoria, may be said to be all stomach, as they are, some of them, nothing but contractile sacs for the reception of alimentary matter which is contained in the water they inhabit. Another view may be taken, which is that these very low animals have no stomachs, and that all the diffestion they perform is a tissue assimilation of organic and mineral matter. They are, however, generally spoken of as having stomachs. In the ecelenterata there is considerable diversity in the structure and relations of the stomach to the other parts, and yet a remarkable unity of plan, which is held by some to be evidence of progressive development; but the existence of a. plan having perfect anal:)gies may not lie regarded as more than the evidence of order; and this is as con sistent with the belief that an organism commenced its zoological life in much the same oondition in which we find it, as with the hypothesis that it has been the subject of a con stant change of type. In the hydrozoa the stomach cavity and body cavity are one. In actinozoa, that which answers to the stomach is a wide tube which empties into the body cavity; but the body cavity acts as a stomach also; and in fact what is usually regarded as a stomach is probably no more than an esophagus or gullet. There is a tendency in actinozoa to the formation of special organs, which means that there is more specialization of organs. In the ecidnodermata, the sub-kingdom which includes the sea-urchins, star-fishes, etc., there is a higher organization generally, as is seen in the radiate nervous system, and iu these animals we find a stomach and an intestinal canal having no communication with the body cavity. In the star-fishes the stomach occupies the whole central part of the body; From it two 10112:, tapering, ramified caeca are given, of opposite the commencement of each ray, and are dis tributed through it in a central line, so that there are ten pairs of email appendages. Insaddition to these the stomach is provided with small, short caeca between the largo trunks in the rays. In the sub-kingdom annulosa the form of the digestive apparatta exhibits much variety. In some orders, as &naida, comprising the tape-worms, there is no stomach, nor even mouth proper. In the order trematoda there is a mouth and an alimentary canal, and consequently an arrangement which answers for a stomach. but there is only one aperture for the entrance of food and expulsion of fmces. In the second division of annulosa, viz., in nenuttelmia, there are in the first order aeantho eephala, internal parasites without mouth or alimentary canal, but with proboscis and suetorial apparatus. In the next order gordiacea', comprising animals which during a portion of their existence arc parasitic insects, there is sometimes an imperfectly developed digestive apparatus, or none. In the next order, nematoda, including the hunbrieroid worms which infest the alimentary canal of mammals, there are well-developed digestive organs suspended freely in a body cavity, and provided with a mouth and excretory orifice. In the sub-class rotifera (wheel animalcules) there is a complex organization with a ganglionic nervous system. The stomach is large and weil
developed, but there are no organs of blood circulation or of respiration, although there is a corpusculated fluid in the body cavity. Among the anuelides the common leech has an extensive 4igestive apparatus, the stomach not only being large and run ning nearly the whole length etf the body, but provided with eleven capacious caeca.
In the crustaceans, particularly the lobster, the digestive organs are elaborate. The apparatus for mastication is efficient, and the mouth opens by a very short narrow gullet into a capacious stomach in which there are a great number of very minute teeth, and in addition three very large calcareous teeth situated near the pyloric orifice. A number of strong, calcareous bones, longitudinal iu direction, support the membranous portion of the stomach, and form a basis for the support of the large teeth. The entire organ is covered externally with a layer of muscles of great power. Two of the large teeth resemble the molars of an elephant, and they have a sort of rotary molar motion. Between them is the third large tooth, which has a rounded surface, and assists in mastication by constantly pushing the food.between the molars. The whole of this apparatus is called " the lady in the lobster." Some insects have even more elabo rate stomachs than crustaceans. The locust has a marvelous masticating and digest ing organism. See LOCUST and GRASSHOPPER, General Anatomy, vol. IX. p. 123. They seem to be furnished with all possible accessories for the trituration and solution of the coarse food upon which they live. The coleoptera are, as an order, perhaps possessed of more powerful digestive apparatus than the orthoptera, some of the beetles almost equaling, the acrididte. They have a crop, a gizzard, and a chylific stomach, and are enormous eaters, as every housekeeper knows who has lied experience with eroton bugs and cockroaches, and every farmer who has defended his potato crop against the ravages of the Colorado beetle. (See POTATO Boo.) The crop and stomach of the honey-bee is a marvelous piece of mechanism. The (esophagus dilates into a large crop, the honey-collecting bag, which is capable of being dilated by muscular action so as to exhaust the nectar from flowers. The true stomach is connected with the .crop in a remarkable manner. It commences by a small tube, which can be inserted into the crop or withdrawn from it. When inserted it is doubled upon itself, forming a shut valve through which the honey cannot pass. The bee feeds itself at will by withdraw ing the tubular portion of the true stomach, when the contenta of the crop are permitted to pass into it. In the molltisca the stomach and alimentary canal are often simple in structure, but efficient; for digestive fluids are furnished in great abundance. The rapid growth of the oyster is evidence of its power of digestion and assimilation. In sonic of the gasteropod mollusks the stomach is more complex, being often provided with cartilaginous or calcareous plates for the trituration of food. Distinct salivary glands are usually present, and the liver is well developed. The cephalopod mollusks, as the cuttle fishes and octopus, have enormously efficient digestive apparatus. See CEPHALOPOD-v, a nte.