ORGANS OF SECRETION. 587 



more easily sent to all their minutest subdivisions. In the 

 simplest forms of the chylopoietic and intestinal glands in 

 the lower articulata, the analogies of these minute secreting 

 tubuli were determined chiefly by the parts of the alimentary 

 canal into which they open, the salivary follicles opening into 

 the mouth or oesophagus, the hepatic, gastric, and pancreatic 

 into the long cavity of the stomach, and the urinary into the 

 terminal or cloacal part of the intestine. 



In the Crustacea, however, not only are the different parts 

 of the digestive canal more denned, but the character of the 

 glands is also more distinct and obvious. From their aqueous 

 habitat and the moist condition of their food, these animals, 

 like fishes and cetacea, require no salivary glands, and rarely 

 present a rudiment of these organs even in the highest 

 decapods ; the pancreatic glands, so nearly allied to them in 

 function, follow nearly the same law of development, and 

 only equivocal traces of them are perceptible in some of the 

 entomostracous and higher species ; and the rudimentary 

 condition of these two important chylopoietic glands, corres- 

 ponds also with the nutritious character of the food of these 

 predaceous inhabitants of the waters. The chemical part of 

 their digestive process depends, therefore, almost entirely on 

 the liver, which is generally of great magnitude, minutely 

 subdivided, and possessed of an immense secreting surface, 

 as in the aquatic mollusca. 



In the lower forms of amphipodous and isopodous 

 Crustacea, two or three pairs of isolated simple biliary tubuli 

 opening into the elongated stomach, still compose the entire 

 liver, as in insects ; and in the simplest parasitic species, this 

 organ is represented merely by a follicular development, or 

 cellular covering, investing the parietes of the stomach, as in 

 some of the annelides. The liver in the higher orders con- 

 sists generally of a single duct on each side of the stomach, 

 more or less subdivided and ramified, and with its ultimate 

 tubuli disposed with perceptible symmetry, in lobules and 

 lobes. In the most developed forms of decapods, both ma- 

 crourous and hrachyourous, the mass of small, short, straight, 

 parallel tubuli biliferi arranged in lobules, and these in larger 

 lobes, constitutes the largest organ of the body. These 

 innumerable hepatic coeca are the terminal ramifications of 

 two short wide ducts, which open into the narrow muscular 



