Gastrocnemius

“ The animal which has been seen to hatch from the egg of entoconcha is a young gasteropod, which, like the young of ordinary forms, has a spiral shell, a muscular locomotor foot, tentacles, eyes, hearing organs, and a nervous system like that of other gasteropods at the same stage of growth. The digestive tract is divided into regions, like those of an ordinary gasteropod, and the young entoconcha has no peculiarities to indicate that the structure and habits of the adult are to be in any way strange or unusual ”

“ It should be to the right of the anus were this the case. Spengel showed that the parabranchia of Gastropods is the typical olfactory organ or osphradium in a highly developed condition. The minute structure of the epithelium which clothes it, as well as the origin of the nerve which is distributed to the parabranchia, proves it to be the same organ which is found universally in molluscs at the base of each gill-plume, and tests the indrawn current of water by the sense of smell. The nerve to this organ is given off from the superior (original right, see fig. 3) visceral ganglion. ”

“ The male is smaller. They are found in the caecum and rectum of man, and cause great irritation and sometimes serious functional disturbance. The eggs are laid in immense numbers but perish in water. If whilst still in the egg-shell the larvae are swallowed on fruit or raw vegetables, etc., they are set free in the stomach and small intestine by the action of the digestive secretions. The distribution of this parasite is universal. Besides numerous species that inhabit the alimentary canal of Vertebrates, such as O. ambigua Rud., found in hares and rabbits ”

“ When the mouth organs are removed, there will be no difficulty in taking out the stomach. This should be cut open with a needle, and then we shall see the gastric teeth (g g) which grind up the food against the fixed calcareous plate (b b) . The lower end of the stomach is set with fine hairs, which prevent the passage of food into the intestines until it has been ground fine between these living millstones. A similar arrangement is found in all the higher Crustacea. The time spent in comparing the gastric mill of the Crab with the ‘gizzard’ of the Cockroach will not be thrown away. ”

“ Whilst in all other reptiles the gut, at least stomach, liver and mid gut, are suspended by the mesentery from the vertebral column and hang free into the body cavity, in some snakes, especially often described in Boa and Python, the body cavity is cut up into numerous spaces, by peritoneal folds which connect neighbouring twists of the canal into bundles and attach them to the ventral surface of the body-wall. Probably the gut is thereby secured against dislocations in adaptation to the peculiar twisting contortions of the body, especially in the act of climbing. ”

“ As for the effect on man, there is little foundation for the fear with which centipedes are regarded. Our native species produce, at most, local symptoms,—sometimes severe local pain and swelling,—but there is no authentic record of fatal results. In the tropics, some of the species attain a large size, Scolopendra gigantea reaching a length of nearly a foot. These forms are justly feared, and there is good evidence that death sometimes, though rarely, results from their bite. ”

“ When present, they generally involve the peritoneum or the mesenteric glands. The liver is sometimes attacked, the stomach rarely.
Benign tumours are not of common occurrence in the digestive organs. Simple growths of the salivary glands, cysts of the pancreas and polypoid tumours of the rectum are the most frequent.
The intestinal canal is the habitat of the majority of animal parasites found in man. Frequently their presence leads to no morbid symptoms, local or general ”

“ When articles of food are in a partial state of putrefaction, so that the antiseptic properties of the gastric juice cannot be quickly enough brought into play, there is a rapid fermentation in the stomach, with the development of symptoms of gastric and subsequently of intestinal catarrh. Unripe fruit, vegetables composed of hard tissue, as early potatoes, cucumbers, pineapples, and cherries, by their indigestible nature, are frequent causes. Oysters, crabs, fish, and lobsters often occasion acute diarrhoea in consequence of being in an unfit condition for food. ”

“ When a living animal of a relatively small size comes within range of the tentacles, it appears to be suddenly paralysed by the action of the nematocysts and held fast. The tentacles in contact with it, and others in the neighbourhood but to a lesser extent, then bend inwards, carrying the prey to the mouth. The passage of the food through the stomodaeum is effected partly by ciliary, and partly by muscular action, and the food is then brought to the region of the mesenteric filaments where it is rapidly disintegrated by the digestive fluids they secrete. ”

“ The hinder end of the gullet is produced into a short, wide, membranous funnel projecting freely into the midgut or stomach. The latter is elongated and oval, composed of four rows of hexagonal cells, with large nuclei. This is separated by a distinct constriction or sphincter from the short pear-shaped rectum, which opens by a minute anus on the back just in front of the pedal processes.
The food is chiefly organic débris; but Gastrotricha have been seen to attack large Infusoria by nibbling, and to swallow the protoplasm as it exudes from the wound in their prey. ”

“ The Gastropoda are mainly characterized by a loss of symmetry, produced by torsion of the visceral sac. This torsion may be resolved into two successive movements. The first is a ventral flexure in the antero-posterior or sagittal plane; the result of this is to approximate the two ends of the alimentary canal. In development, the openings of the mantle-cavity and the anus are always originally posterior; later they are brought forward ventrally. During this first movement flexure is also produced by the coiling of the visceral sac and shell ”

“ The transition into the stomach is quite gradual. The latter is strongly muscular, partly transversely placed, and possesses often a very distinct pyloric stomach. In Chelone conical papillae extend into the cardiac portion. In the majority of tortoises the inner lining shows longitudinal folds with numerous small glands, mucous and gastric, but their distribution differs much in the various families and even genera. The lining of the mid gut shows either longitudinal folds or a network, without glands, except in some cases, Lieberkühn crypts, e.g. in Trionyx, not in Testudo and Chelone. ”

“ Worms.—Intestinal parasites are symptoms rather than a cause of defective digestion, and drastic medicines (calomel, Glauber's-salt, etc.) are merely palliatives; even a change of diet may fail to afford permanent relief if the general mode of life favors a costive condition of the bowels. Like maggots, maw-worms seem to thrive only on putrescent substances, on accumulated ingesta in a state of self-decomposition, and disappear as soon as exercise, cold fresh air, and a frugal diet have reestablished the functional vigor of the digestive organs. ”

“ The salivary glands are frequently wanting in marine animals; the water swallowed with the food taking the place of saliva. The liver and other appendages to the digestive tract are wanting in many of the lower animals, and a parasitic life may entirely do away with the need for them, even in an animal which belongs to a highly-specialized group. The ordinary gasteropod mollusks have digestive organs which are almost as highly specialized as those of a vertebrate ”

“ In most Gasteropoda the liver consists of two distinct lobes, between which are embedded the stomach and part of the intestine. In many Nudibranchiata the liver becomes ‘diffused’ or broken up into a number of small diverticula or glands connecting with the stomach and intestine. The so-called cerata or dorsal lobes in the Aeolididae are in effect an external liver, the removal of which to the outside of the body gives the creature additional stomach-room. ”

“ Towards the pyloric end of the stomach the true gastric glands are often replaced by mucous glands. There are, nevertheless, not a few Teleosts in which special gastric glands are absent, as, for example, Syngnathus acus, and several species of Cyprinidae, Labridae, and Blenniidae, etc. In at least two genera (Gastrosteus and Cobitis) , belonging to widely different families, gastric glands are present in certain species but absent in others. ”

“ It is really astonishing to see what large morsels they can dispose of with the assistance of their extensile mouths and stomachs. It is not even necessary, indeed, that the morsel be so small as to be entirely enclosed by the walls of its digestive cavity, for the anemone will digest one portion while the other remains projecting beyond its mouth. Further, it will even attack bodies which it cannot swallow at all, by protruding its stomach so as to partially envelope them, and then digesting the portion enclosed. ”

“ When we remember that even man's body, with all its various parts, and the body of all the other higher animals, are built up originally out of these two simple layers, we cannot lay too much stress on the phylogenetic significance of this gastrulation. In the simple primitive gut or gastric cavity of the gastrula and its rudimentary mouth we have the first real organ of the animal frame in the morphological sense; all the other organs were developed afterwards from these. In reality, the whole body of the gastrula is merely a "primitive gut." ”

“ The archenteron becomes the gastrovascular system or coelenteron. Between the ectoderm and endoderm a gelatinous supporting layer, termed the mesogloea, makes its appearance. The gastrula has now become an actinula, which may be termed the distinctive larva of the Cnidaria, and doubtless represents in a transitory manner the common ancestor of the group. In no case known, however, does the actinula become the adult, sexually mature individual, but always undergoes further modifications, whereby it develops into either a polyp or a medusa. ”

“ This gizzard has not the same function in all cases, for whereas in some forms (e. g., in Bowerbankia) it is lined with horny projections and is a powerful crushing organ, in others (e. g., in Hislopia or Victorella) it acts as an antechamber in which food can be preserved without being crushed until it is required for digestion, or rough indigestible particles can be retained which would injure the delicate walls of the stomach.
Digestion takes place mainly in the stomach, the walls of which are of a glandular nature. ”

“ The ventral sucker is concealed, but the transparency of the skin permits a view of the internal organs.
Another remarkable genus, established by Von Siebold, is Gasterostoma. In this genus the ventral sucker has taken the position usually assigned to the oral opening; the latter being near the centre of the body. The digestive cæca also disappear, leaving only a short stomachal cavity, which reminds one of the same viscus in imperfectly organised sporocysts or rediæ. When G. gracilescens first came under my observation I followed Rudolphi in describing it as a distome (D. gracilescens) . ”

“ Not a few may also be found in the intestinal canal and in the excrement about to be voided. Occasionally dead specimens become surrounded by inspissated bile, and gritty particles deposited in the liver ducts, thus forming the nuclei of gall-stones. Mr Simonds mentions a remarkable instance, “where the concretion was as large as an ordinary hen’s egg, and when broken up was found to contain about a dozen dead flukes. It was lying in a pouch-like cavity of one of the biliary ducts.”
In respect of treatment we all know that “prevention is better than cure.” ”

“ The gastric appendages are shorter and wider, and are provided with stomata, which are applied to the prey, seized and benumbed by the tentacles. If the prey be small, it is sucked bodily into the gastric sac; if large the sac becomes distended with its juices and dissolved parts, the gastric secretion being a very rapid and powerful solvent. ”

“ The larger spines often pass out by perforating passages through the wall of the intestine and through the body-wall. The aperture thus formed appears speedily to heal after the foreign body has been extruded.
The carnivorous habits of Nemertines even extend to cannibalism, and when kept in confinement they frequently devour one another. For this reason it is unsafe to keep large and small kinds together, as the small ones speedily disappear, being used as food material by the large. If one be divided into several pieces, the pieces are very rapidly demolished by other individuals. ”

“ This is the reason why certain worms are able to exist in the stomach of man and other animals; and if it were possible for an oyster swallowed directly from the shell to continue to live, it would also effectually resist every attempt at digestion. But it, in common with most other beings, soon perishes in circumstances so foreign to its habits; and when once dead, the gastric juice assumes the mastery, and speedily converts it into chyme. ”

“ If the parasites have gained admission to the muscles all hope of destroying them is at an end; but if a person suspects himself to have eaten diseased or trichinised meat he should lose no time in seeking professional assistance, seeing that the administration of suitable anthelmintics might be the means of saving his life, whereas a few days’ delay would probably prove fatal. So long as the worms remain in the stomach or intestinal canal they can be got rid of, but when once the trichinal brood have invaded the flesh then they cannot be expelled. ”