ORGANS OF SECRETION. 589 



.mastication, require a greater development and a more com- 

 plex condition of the chylopoietic glands, than in the active 

 and predaceous articulated tribes. Their slowness of motion 

 or fixed condition, and their aqueous medium, are incompati- 

 ble with many of the glands connected with the organs of 

 relation, developed in the air-breathing animals of the former 

 subkingdom, as the poison-glands of myriapods, insects and 

 arachnida, the cutaneous follicles for odorous or acrid secre- 

 tions to be poured on the surface of the skin, the filamentous 

 glands for the webs of spiders, or the cocoons of insects. 

 The molluscous animals are, therefore, provided with few 

 secreting organs not immediately connected with nutrition 

 or generation, and the great chylopoietic glands, the hepatic 

 and salivary, are remarkable for their size, their constancy, 

 and their conglomerate character, in this great subkingdom of 

 aquatic animals. The liver is always contiguous to the 

 stomach, and opens directly, for the most part by numerous 

 wide orifices, into its cavity. The salivary glands are some- 

 times simple tubuli, sometimes conglobate clusters of short 

 follicles, sometimes both these forms occur together, and 

 they open generally by long ducts into the cavity of the 

 mouth. The pancreas presents both the tubular and lobu- 

 lated forms, opening, like the liver, into the cavity of 

 the stomach, and the urinary organs terminate near the 

 anus. 



In the tunicated animals those glands only are developed, 

 which are most essential to digestion and generation. The 

 small short tubuli biliferi, sometimes as isolated follicles, and 

 sometimes composing lobules, closely surround the greater 

 portion of their stomach, and open into its cavity by nume- 

 rous orifices ; so that the liver in these lowest of the mollusca, 

 presents nearly the divided and the concentrated forms, the 

 two extremes of development, met with in the aquatic 

 articulata, the lowest annelides and the highest Crustacea. 

 No salivary or pancreatic glands are perceptible here, or in 

 the allied conchiferous mollusca. Besides their common 

 genital glands, and the secretions of their mucous surfaces, 

 pallial and intestinal, and the bright luminosity exhibited by 

 many of the species, as salpa and pyrosoma, many of these 

 animals attach to the exterior surface of their tunic, by means 



