116 
DR. C. H. JONES ON THE STRUCTURE 
sometimes discernible, especially when the secretion is in small quantity. These 
cells usually cohere together, yet retaining perfectly their separate outline ; but some- 
times the groups seem to become fused together, and to form a mass which is applied 
against the intestinal wall by a covering membrane. It seems quite certain that these 
cells are naked, and uncontained in any follicular offsets from the intestine ; nor 
does there appear to be any provision for the transmission of the secretion thither ; 
that they perform the function of a liver is I think highly probable ; their appearance 
is generally such that one can scarcely hesitate to believe them to be agents of 
biliary secretion, and I cannot find any other apparatus which seems at all adapted 
to fulfill such an office. However, I must state that in some cases, especially when 
the Daphnia is laden with ova, these cells are almost devoid of their biliary-looking 
contents, and are much less manifest, though even then themselves or their nuclei 
are discernible more or less clearly. IStill, as it is impossible to believe that they ean 
be merely adipose tissue, I regard them as of hepatic nature, and would refer to them 
as an interesting example of a purely parenchymal hepatic organ. 
As a specimen of the liver among Arachnidans, I believe that of the common house 
spider may be referred to ; here the liver is very bulky indeed, occupying the greater 
part of the pouch-like abdomen ; it is of a dull yellowish-white colour. In structure 
it consists of short csecal follicles very closely set together, about -g^th of an inch in 
diameter ; each of these is bounded by a well-marked limitary membrane, and stuffed 
with opake contents. The cells in the interior of the follicles measure about 
to iwfh of an inch ; they have a very delicate envelope, and contain a quantity of 
opake oily-looking matter, with one or more granular but highly refracting vesicles; 
these are usually -3:r^^oth of an inch in diameter, and appear subsequently, when set 
free, to undergo development into secreting cells. There is a good deal of free oily 
matter, but very little trace of bile pigment ; the oily matter very often appears in 
the form of groups of small equal-sized vesicles of an inch diameter, which 
almost seem to be enclosed in a definite envelope ; this may be the commencement 
of the formation of nuclei or young cells under the favouring physical conditions, 
which Ascherson has pointed out. The large size of the gland in this class is worth 
noticing, as well as the character of its contents, which consist principally of granular 
and oily matter. 
Among the various families of the Mollusca, the follicular type of arrangement of 
the liver obtains, I believe, universally ; the gland is remarkable in most cases for its 
large size, and frequently for the deep colour of its elaborated contents. In most 
cases the basement membrane of the follicles is extremely distinct, but occasionally 
it is very delicate, and even its existence has sometimes appeared to me doubtful; 
this led me originally to believe that the presence of the basement membrane was 
not essential to the act of secretion, but that its function was of a purely mechanical 
nature, supporting the secreting cells, and preserving constantly a passage to the 
excretory duct. Subsequent observations have quite confirmed this opinion, by 
