THE LIVER IN ANIMALS. 



593 



of an open framework, supporting aggregations of astomatous amoebiform 

 masses of sarcode, each of which ^directly assimilates food. In the solitary 

 amoeba, and its allies, the proteiform contractile sarcode applies itself to nu- 

 trient substances, and completely incloses them ; digestion and assimilation 

 take place within it, and the undigested portions are extruded at some indif- 

 ferent point. The Rhizopods are nourished in a similar manner. The micro- 

 scopic parasitic Gregarinida, appear like the Tsenia and Echinococci, to imbibe 

 nutrient matter directly by their surface, from the fluids of the intestine, 

 perivisceral cavity, or other chambers or tissues of the animal in which they 

 live. 



The Abdominal Digestive Glands. 



Gastric Glands. Gastric tubuli exist in the secreting portion of the stom- 

 achs of all the Yertebrata, becoming short and simple in the frogs and fishes. 

 In the higher Mollusca and Annulosa, as in the Cephalopods, Pteropods, and 

 perfect Insects, the stomach also has numerous follicles, probably analogous 

 to gastric tubuli ; but in the lower Mollusca and Annulosa, and in the Mol- 

 luscoida and Annuloida, the walls of the gastric cavities are often destitute of 

 distinct glands. This is the case also with the walls of the digestive canal in 

 the Coelenterata. 



Liver. This important organ, or some representative of it, is more widely 

 distributed amongst animals than any other secreting or excreting gland. It 

 is present as a well-defined organ, not only in all the Yertebrata, the .amphi- 

 oxus only excepted, but also in all the Mollusca and Molluscoida, and is rep- 

 resented in the Annulosa by tubular caeca or follicles, which are found even in 

 the Annelida, and likewise in the Eotifera and Echinodermata amongst the 

 Annuloida. No corresponding part, however, exists in those Annuloida 

 which are destitute of a distinct alimentary canal, such as the Trematoda, 

 Tseniada, and Acanthocephala, nor yet in the Coelenterata, much less in the 

 Protozoa. 



Amongst the Yertebrata, the liver, proportionally to the body, becomes 

 progressively larger in passing from the Mammal to the Fish. Its general 

 form corresponds with that of the abdominal cavity : thus, it is broad in the 

 apes and the Carnivora, longer in the larger Euminant and long-bodied ani- 

 mals ; of moderate length in Birds ; broader in the comparatively short Che- 

 Ionia and Sauria, but long in the elongated Ophidia ; broad and short in the 

 frogs and toads, but long in the newts ; stretching widely into the abdomen 

 of the broad-shaped skates and rays, but lengthened out in the eel. Its posi- 

 tion is usually symmetrical, but in the Mammalia with large compound 

 stomachs, it is placed more towards the right side, as is also the case in the 

 anthropoid apes ; in Fishes, generally, it lies more on the left side of the body. 

 In Birds, in which the diaphragm is complete, the liver is notched for the re- 

 ception of the heart and pericardium ; in Reptiles, Amphibia, and Fishes, 

 which have no diaphragm, the liver also reaches up to the pericardium, ex- 

 cept when the body is very long, as in the serpents and eels. 



The liver in the Mammalia generally, is nearly simple, its lobes being only 

 slightly marked. In the Ruminants, it is subdivided into three lobes ; in the 

 Rodentia and Carnivora, there are from three to five lobes, viz., a central one, 

 and one or two on each side ; sometimes it is further subdivided into small 

 and irregular secondary lobules. In the llama, amongst Ruminants, the under 

 surface, and in the capromys, a Rodent animal, the whole surface, is divided 

 by deep fissures into angular masses, resembling those of the kidneys of the 

 bear. In Birds, the lobes are two, and symmetrical ; in Reptiles and Am- 

 phibia, the lobes are also generally two, but the liver is undivided in the 

 Ophidia ; in Fishes, the liver is often more subdivided. The microscopic 

 structure of this gland, in all the Yertebrata, resembles that of the human 

 liver. In the curious amphioxus, a long ceecal appendage from the intestinal 

 canal, having a layer of greenish cells lining its interior, is regarded as a ru- 

 dimentary liver, no distinct organ otherwise existing. 



In the Mollvs'Mj the liver is a large, symmetrical, solid, and lobulated organ, 

 having two 'ducts. Its great development in these animals, and also, it may 



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