446 



SECRETION. 



of them containing scarlet-red, and others 

 bright yellow granules ; the latter are regarded 

 by Dr. W., and probably with justice, as the 

 diffused rudiments of a liver.* In the Boiver- 

 bankia densa, and in other Bryozoa, very 

 distinct spots may be seen in the parietes of 

 the stomach, which seem to be composed of 

 clusters of biliary cells contained within fol- 

 licles ; and during digestion, the contents of 

 the stomach are seen to be tinged with a rich 

 yellow-brown hue, derived from the matter 

 discharged from these follicles. -f- In the 

 Asterias the digestive cavity is surrounded by 

 a more complicated glandular apparatus, but 

 it seems difficult to determine the precise 

 portion of this which discharges the function 

 of a liver. The central stomach is furnished 

 with a pair of glandular appendages, each 

 composed of a cluster of follicles, which open 

 into its fundus ; and these, from their dull 

 yellow colour, have been thought to be a 

 liver. Dr. Williams states, however (loc. 

 cit.), that their ultimate structure does not 

 sanction that idea, the terminal vesicles 

 abounding in a white elastic tissue, in the 

 meshes of which are entangled a number of 

 small, compact, and granular cells, which are 

 by no means hepatic in their aspect. He is 

 disposed to agree with Dr. Grant, who hints 

 that this organ may be a rudimentary pan- 

 creas ; we should, ourselves, regard it as more 

 probably a salivary gland, its secretion being 

 apparently mingled with the food immediately 

 upon the ingestion of the latter. In the 

 walls of this central stomach, proper gastric 

 follicles have been detected by Dr. Williams; 

 and he regards in the light of an hepatic organ 

 the dilated culs-de-sac, rilled with large glan- 

 dular cells, which are disposed in great num- 

 bers along the ramifying caeca! prolongations 

 of the central stomach that are extended into 

 the rays. 



In the lower groups of the Articulated 

 series, we meet with a diffused form of the 

 biliary apparatus, not unlike that which has 

 been just described in the lower Radiata. 

 Thus in the Earthworm, the large annulated 

 alimentary canal is completely encased in a 

 flocculent external coating, which, when exa- 

 mined with the microscope, is found to consist 

 of a mass of minute flask-shaped follicles, 

 held by tubular peduncles, several of which 

 coalesce to form the excretory canals for the 

 discharge of the secretion into the digestive 

 cavity. These follicles are composed of a 

 membrane of extreme tenuity, and their inte- 

 rior is rilled with cells containing granular 

 matter and oil globules, which are the consti- 

 tuents of the hepatic secretion. In the Leech 

 and some other Annelida, the alimentary canal 

 is furnished with large sacculated appendages ; 

 and in the walls of these, as well as of the 

 central canal, the biliary cells are closely dis- 

 posed. These cells, according to Dr. Wil- 

 liams, are not included within follicles, as in 

 the earthworm ; the absence of csecal multi- 



* Guy's Hospital Reports, 1846, p. 280. 

 t Dr. A. Farre, in Phil. Trans. 1837. 



plications of the stomach in the latter being 

 compensated by a concentration of parts in 



Fig. 310. (Fig. 69. Vol. I.) 



Alimentary canal of Leech, with ccecal prolongations. 



the biliary system. In the Mympoda, there 

 is a decided advance from this diffused form 

 of hepatic structure, towards that more con- 

 centrated and isolated condition, in which we 

 find the liver of Insects. The general distri- 

 bution of the biliary organs in this class has 

 already been described. (See INSECTS, Vol. II. 

 p. 974.) They consist of a number of dis- 

 tinct filiform tubes, usually of a yellowish- 

 brown colour, placed in close apposition to 

 the sides of the alimentary canal, and opening 

 into it near the pyloric extremity of the 

 stomach, usually by separate orifices, but 

 sometimes after the junction of two or more 

 with each other, to form short common 

 trunks. Their number varies considerably; 

 the fewest, namely four, existing in the Dip- 

 tera, six being found in the Lepidoptera, and 

 many more in the Orthoptera and Hymenop- 

 tera. When few in number, they are very 

 long, sometimes three or four times the length 

 of the alimentary canal, and are tortuous and 

 convoluted ; when numerous, they are pro- 

 portionally short, and are more delicate in 

 structure. In many larvae, they are furnished 

 with lateral caeca, but these almost always 

 disappear as the insect approaches the imago 

 state. The following is the description re- 

 cently given of the minute structure of the 

 biliary tubuli, by a well qualified observer : 

 " When more intimately examined, these 

 tubes are found to consist of a delicate tube 

 of clear, transparent, amorphous basement 

 membrane, the inner surface of which is co- 

 vered with secreting cells. From the thin- 

 ness of the tube, the cells often project, so as 

 to give it a granulated appearance when 



