416 THE SOLIDS. 



discernible without glasses ; and these again are still further 

 subdivided into other cells very numerous, and which are 

 only to be seen with the aid of the microscope. It is these 

 last which constitute the follicles of the mucous membrane 

 of the gall-bladder, which differ, however, greatly from the 

 ordinary tubular follicles of compound mucous membranes, 

 being simple cells or depressions formed by the plaited and 

 ridged arrangement of the membrane of the gall-bladder. The 

 follicles in the hepatic duct, and also in the inner tunic of the 

 vesiculae seminales, would appear to be of the same character. 



If air be inserted, by means of the blow-pipe, beneath the 

 mucous coat, the latter will be thrown up into lobes, each 

 of which corresponds with one of the larger honeycomb cells: 

 this fact shows that the mucous membrane of the gall- 

 bladder is bound down to the fibrous tissue beneath, prin- 

 cipally in the intervals between the cellular depressions 

 alluded to. 



Injection thrown into the ductus communis choledochus 

 very frequently reaches the coats of the gall-bladder : this 

 fact affords an interesting and striking proof that the vessels 

 ordinarily injected from the common hepatic duct are not 

 biliary, for it is generally acknowledged that biliary ducts do 

 not exist in this situation, a conclusion to which one, with- 

 out hesitation, arrives, on reflecting that in such a situation 

 they could serve no possible purpose. 



General Remarks. Should the foregoing account of the 

 mode of termination of the biliary ducts be correct, of which 

 scarcely a reasonable doubt can be entertained, it is evident 

 that in the vertebrate class of animals, at least, the liver is 

 not of the follicular type, and that in them this organ should 

 be separated from those glands formed on the follicular type. 

 In the fact of the secretion making its way into closed vessels, 

 the liver clearly manifests an intimate and essential relation- 

 ship with the vascular glands. 



The liver, then, in the vertebrate series, is the only excep- 

 tion, with which we are at present acquainted, of an organ 

 which, being furnished with an excretory duct, is yet not 

 formed on the follicular plan of development. 



