594 SPECIAL PHYSIOLOGY. 



be added, in the cold-blooded Vertebrata, may be connected with the function 

 of storing up fatty matter, as the adipose tissue does in the higher Mammalia. 

 The nucleated hepatic cells in the Non-vertebrate animals, and also in the 

 cold-blooded Vertebrata, contain much more simple oleaginous matter than 

 they do in the warm-blooded Vertebrata, in which latter the proper biliary 

 fatty acids chiefly occupy the cells ; in Birds, the cells contain less ordinary 

 fat than in Mammals. Sometimes, as in the Cephalopods and Lamellibran- 

 chiata, the liver is subdivided into minute lobules, composed of branching 

 ducts, ending in dilatations. In the Gasteropods, the ramified ducts and 

 terminal follicles are more distinct, so as to form a loose compound racemose 

 gland. The chief ducts are ciliated internally. 



Amongst the Molluscoida, the Brachiopoda have a large, minutely lobu- 

 lated liver, composed of ramified tubuli. As some of the earliest fossils yet 

 discovered belong to this Class, an hepatic organ yielding bile, and, therefore, 

 digestive processes corresponding with those known to us in the present day, 

 must have existed in most remote periods of the earth's history. In the As- 

 cidioida, the liver presents interesting gradations ; for, in different cases, it 

 may consist of a small gland, a cluster of follicles, a single follicle, or simple 

 lacunae or laminae on the inner side of the intestine ; it is represented only by 

 a yellowish, orange-colored, or brownish glandular spot, on the hepatic portion 

 of the walls of the intestine. In the Polyzoa, the sides of the intestine below 

 the stomach are marked with brown hepatic tubes, follicles, or spots. 



Amongst the Annulosa, the Crustacean liver is of a yellowish color, large and 

 complex. In some kinds, as in squilla, it is symmetrical, lobulated, and sub- 

 lobulated, each sublobule consisting of clusters of round follicles connected with 

 a central duct. In the crabs and lobsters, the follicles of the liver are innu- 

 merable, much branched, and separated from each other. In the river crab, 

 the follicles are less ramified. In the lowest Crustaceans, such as the parasitic 

 argulus, the hepatic follicles are still more simple, or this organ consists only 

 of a mass of nucleated cells. 



In the highest Insects, and in the Mj^riapods, the liver is represented by 

 hepatic tubuli, connected with the intestine ; these are short and numerous in 

 dytiscus, only two, but elongated, in blaps, or even single, as in the grasshop- 

 pers ; sometimes they are mere vesicles. In no case is the liver massive, but 

 always tubular. In the Spiders, the hepatic follicles are either short and sim- 

 ple, or they end in compact clusters of vesicles. In the Annelids, the liver is 

 represented by gland cells, situated either in ramified tubes, as in Arenicola, 

 or in tubuli ending in an oval sac, as in Aphrodita, or in numerous follicles, 

 as in the leech. 



Amongst the Annuloida, a single long follicle in the Trematode worms, rep- 

 resents the simplest form of rudimentary liver ; in the parasitic Tseniada and 

 Echinococci, the liver, as indeed the intestine itself, is unrepresented. In cer- 

 tain Echinodermata, as in asterias, colored cells are found in the walls of the 

 radiating prolongations of the gastric cavity, which perhaps secrete biliary 

 matter. 



In the Coelenterata, no separate hepatic organ exists in connection with the 

 simple digestive cavity ; but the walls of this, as in velella, sometimes present 

 a mass of gland cells, which may form bile. No such product has yet been 

 found in any part of the unicellular Protozoa. 



Bloodvessels of the Liver. In all the Vertebrata, the liver receives blood both 

 from the hepatic artery and the portal vein. In the Mammalia, this vein, as 

 in Man, has only a few communications with the lumbar and pelvic svstemic 

 veins. In Birds and Reptiles, the connection between the pelvic and portal 

 veins is such, that a part of the blood from the lower extremities, and from the 

 tail, joins the portal blood, and passes into the liver. In Fishes, the caudal 

 veins, and sometimes those from the reproductive organs and the air-bladder, 

 are connected with the portal system. In the Mollusca, the liver is supplied 

 solely with arterial blood ; the same is the case also in the Annulosa and 

 Crustacea, indeed, in all Non-vertebrated animals which have bloodvessels. 



Gall-bladder. In Mammalia, a gall-bladder is sometimes present, and some- 

 times absent. Amongst the herbivorous kinds, it is present in nearly all Ru- 

 minants, as in oxen, sheep, goats, and antelopes, but not in the camels and 



