114 
DR. C. H, JONES ON THE STRUCTURE 
material of the secretion from a previously formed granular blastema. The contents 
of the tubes are for the most part free in the cavity, and form a continuous layer 
along the wall ; but sometimes, especially in the sacculated tubes of the fly, the cells 
and granular matter form separate masses, though these are not I think surrounded 
by envelopes*. The central canal varies much in width ; sometimes it is very narrow 
or obstructed with oily or biliary matter, in other cases it is equal to half the dia- 
meter of the tube. 
Directing our attention now to the so-called adipose tissue, which I will venture 
to name the parenchymal portion of the liver, it is to be observed that it varies a 
good deal both in its extent and in its general appearance in different instances ; 
moreover, it is not always uniform throughout, but presents in different parts succes- 
sive stages of development. In its simplest and primary state, it appears as a pale, 
granular and amorphous blastema, containing numerous large cells, the average 
diameter of which is y^th of an inch ; these are provided with a distinct envelope 
enclosing well-formed nuclei and granular matter of a yellowish tinge. Very nume- 
rous young cells are also present in the blastema ; they are nucleated, and contain 
only pale granular matter ; their diameter varies from 3 _ 2^o ¥ o of an inch ; lastly, oil- 
globules of a greenish yellow tinge, some large and others of minute size grouped 
together, are also found in this material ; these seem clearly to arise from the blas- 
tema and not to be produced in cells, in which they are never found. Following on 
now the development of the parenchyma, we find that a mass of granular blastema, 
in which lie both young and fully-formed cells, assumes a definite form, its margin 
becomes even and invested by an homogeneous membrane ; thus we have produced 
vesicles, or short tubes of various size and shape, which coalesce very irregularly with 
each other, and form a kind of coarse net-work. Occasionally the vesicles are found 
free and unconnected with others ; sometimes also they are replaced more or less 
completely by long tubes, which might easily be mistaken for the hepatic tubes them- 
selves. The contents of the vesicles or tubes vary a good deal ; in Caterpillars they 
are wholly filled with large colourless oil-drops ; in Butterflies, May bugs, and some 
other insects, they contain a quantity of yellow biliary-looking matter, with various 
proportions of oily and granular matter. In some cases there is scarce any oily matter 
at all, but only granular, pale, or of a yellow tint. The primary cells may almost always 
be discerned in the interior of the vesicles, and upon them doubtless depend the 
persistent action of these structures. The interesting observation of Dr. Williams, 
respecting the termination of minute tracheary ramifications in the vesicles of moths 
and butterflies, I have been able in some measure to confirm : I cannot speak posi- 
tively as to the tracheae actually terminating in the vesicles, but I have seen them 
traversing an elongated vesicle from one end to the other, and thus holding nearly 
as intimate a relation to the contents as if they had actually terminated in them. 
* Dr. Williams describes, as the constant arrangement of the contents of the tubes, large cells containing 
several secondary ones with granular and biliary matter. 
