SECRETION. 



449 



'02 inillim. in diameter; those towards the stomach gives off on either side a number of 

 other extremity about '01 millim. Some of branches, which usually redivide, and then 



Fig. 31 J .. 



Fi->. 315. 



Hepatic cells of Helix albolabris. 



a, 1, 2, two cells from the bottom of the cajcum ; 

 b, 1, 2, two cells more advanced, containing nu- 

 merous oil globules ; e, 1, 2, 3, three cells, con- 

 taining larger oil globules ; d, a cell distended 

 with oil ; e, a cell containing nothing but six 

 deep yellow consistent oil globules ; f, a cell con- 

 taining a hard yellow mass of fat ; g, a cell rup- 

 turing, and its contents escaping ; ' h, nuclei of 

 hepatic cells, highly magnified. 



the fully ripe cells (A, 1, 2) are filled with 

 innumerable minute globules of oil, hardly 

 distinguishable from the granular matter ; 

 others (c, 1,2,3) with globules of a larger 

 size ; some are found with from one to ten 

 or more large, deep yellow, oil globules in the 

 centre ; a few (/') with a hard or crystallised 

 mass of fat in the centre ; and many (d) are 

 distended with oil. By pressing the cells (g) 

 between two plates of glass, the contents will 

 be squeezed out, and the structure will be 

 seen as follows : the vesicular transparent, 

 amorphous cell-wall, finely granular matter, 

 fat globules, and a granular nucleus (h), mea- 

 suring about '01 millim. and containing a hard 

 transparent nucleolus. A few of the cells 

 contain two nuclei. The blood-vessels, con- 

 sisting of arteries and veins, form a rete around 

 the bulbiform caeca, but do not appear to 

 come in immediate contact with the secreting 

 cells" (loc. cit.). The general plan of struc- 

 ture of the liver of the Cephalopoda is essen- 

 tially the same ; the hepatic ducts and follicles 

 being clustered as in a raceme, and the follicles 

 being crowded with biliary cells. In the 

 Lo/igOy these follicles are described by Dr. 

 Williams (op. cit.), as being themselves sac- 

 culated, by duplications of their membrane ; 

 and some of the biliary cells appear as if pro- 

 ducing a new generation within themselves. 



A verv remarkable departure from the 

 general type is presented by certain of the 

 N IK! ibranc /date Mollusca, of which Eolin may 

 be taken as the type. In these animals, the 



VOL. iv. 



Eolis Farrani, showing the branchial papilla. 

 {After Alder and Hancock.') 



give off smaller tubes, which are continued 

 into the branchial papillae that cover the dor- 

 sal surface (Jig. 315.). "The prolongations 

 of the branches that enter the papillae undergo 

 a considerable enlargement and change of 

 form ; and from the variety and brilliancy of 

 their colouring are the chief attraction of 

 these elegant little animals. The simplest 

 form of this peculiar organ is met with in 

 Eolis conchma, where it is a mere dilated tube, 

 having its walls slightly waved, and the inner 

 surface sprinkled with darkish granules. In 

 E. Farrani {fig. 316. B) it still retains a con- 

 siderable simplicity of structure, but becomes 

 decidedly sacculated. The complexity is 

 much increased in E. olivacea, in which it is 

 produced into puckered follicles or sacculi ; 

 but in E.papillosa (fig. 316. A) it appears to 

 attain its highest development. The central 

 canal is there somewhat tortuous, and gives 

 off on all sides variously sized, irregular, blind 

 sacs, which are crowded with little compound 

 follicles. The whole of the inner surface is 

 lined with a thickish layer of irregular vesicles 

 or globules, filled with numerous granules. 

 These last, when submitted to a high magni- 

 fying power, are seen to be of various sizes, 

 transparent, rounded, and nucleated. The 

 whole of the internal surface of the gland is 

 covered with vibratile cilia. These compound 

 glands are evidently biliary organs, diffused 

 throughout the several papillae, and supplying 

 the place of a compact liver, which is wanting 

 in the body of these animals. The stomach 



G G 



