AND DEVELOPxMENT OF THE LIVER. 
113 
it is wholly parenchymal, in the Sandworm wholly included by the intestinal mem- 
brane, while in the Leech it is of a mixed kind, consisting partly of tubes continuous 
with the intestine and partly of free parenchymal cells. 
In the class of Insects, however widely the external form and the organs of the 
animal functions may vary, the hepatic apparatus preserves a remarkable uniformity, 
consisting' of long slender cylindrical tubes varying in number from 4 to 200. 
Besides these tubes however, of whose truly hepatic character but little if any doubt 
can I think exist, there is another structure whose function is more doubtful; this is 
the so-called adipose tissue, which Mr. Newport believes to serve as a reservoir of 
nutriment, and also to fulfill in some way the office of lymphatic vessels, while Bur- 
MEiSTER, Oken and Treviranus agree in regarding it as a portion of the hepatic 
apparatus. The opinion of these latter authorities is that to which I incline, for 
reasons which I will state, when I have given a description of the structure of the 
two systems of organs now adverted to. The hepatic tubes in the Blow-fly {Musca 
vomitoria) for a considerable part of their course present remarkable dilatations and 
constrictions ; these are sometimes situated so as to face each other on opposite 
sides of the tube, at other parts they are placed more nearly alternate. Towards its 
commencement each tube is found to consist of a number of vesicles, which are 
arranged in a series so as to overlap each other; these vesicles are more or less 
perfectly fused together, their coalescence becoming more complete, and the margin 
more even as we advance towards the intestinal extremity of the tube. In many 
insects the walls of the tubes are perfectly even and present no bulgings or constric- 
tions ; even the terminal blind extremity is, I think, for the most part undilated. A 
most distinct and strongly-marked basement membrane, unsupported by any fibrous 
tissue, but often covered by minute ramifications of tracheae, constitute the wall of 
the tubes ; it is perfectly homogeneous, but presents nothing that I have ever seen 
corresponding to the germinal centres of Mr. Goodsir. On the interior of the base- 
ment membrane is a layer of granular matter of variable thickness ; this is often of 
a deep yellow tint from the presence of biliary matter, or rendered opake for a 
greater or less extent by deposits of oily matter ; in it are imbedded cells which are 
sometimes granular, and exhibit traces of nuclei, especially I think in their early 
stage, but mostly appear as large, delicate and quite transparent vesicles, which often 
escape from their bed of granular matter, and collect in the central canal, along 
which they glide rapidly when subjected to some degree of pressure ; the diameter 
of these varies frotn to of an inch ; they are particularly remarkable from 
the circutnstance that the secretion does not form in them, but under their influence 
probably in the surrounding granular matter. In most instances the layer of granular 
matter is of the same appearance in its whole thickness, but occasionally I have 
noticed that the stratum in contact with the homogeneous tunic was quite pale, 
while that bounding the central canal was more or less deeply tinged with yellow, — 
an interesting difference, which would seem to indicate a gradual evolution of the 
MDCCCXLIX. 
Q 
