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as being full of them. In the next section, we shall find that in the 
Araneids the Malpighian tubules are completely filled with faecal 
“crystals.” We reserve further discussion of this striking parallel 
until we have described the process in the Araneids. 
ARANEIDiE. 
The Araneids are almost the only Arachnids whose digestive 
processes have been investigated, chiefly by Plateau and Bertkau. 
The interpretations of the facts described by these writers require, 
however, to be considerably modified by what we have learnt from 
Obisium and Scorpio. The contents of the so-called liver cells are 
not secretions, but food-globules and their crystal-like remains. How 
near Bertkau came to the recognition of this fact may be gathered 
from his discovery that the cells lining the caeca took in the carmine 
granules which he mixed with water and gave the animals to drink. 
Why then, he asks, should they not also take in “ assimilated nutri- 
ment ” ? — or, we naturally add, the raw food as food-globules ? 
The digesting cells do not all appear to have specialized vacuoles 
as in Euscorpio. Schimkevitch * describes and figures two kinds of 
cells in Epeira, one kind resembling those of Obisium (fig. 1), and 
the other resembling the vacuolated cells of Scorpio (fig. 3). It 
would be interesting to find out in what portions of the gut this 
specialization of the digesting cells takes place. 
The food-globules break down into the typical crystals, the latter 
appearing in two forms, as rather large glassy looking bodies, often 
rod-shaped, and as very minute bodies, which are found massed in the 
bases of the cells, giving this part of the cells a brownish appearance. 
This faecal matter appears to be discharged in two different ways. 
One portion of it is excreted from the cells into the lumen of the gut, 
to find its way down the long narrow tubules into the central canal. 
Another portion appears to pass through the wall of the canal into 
the peritoneal cells , and from these into the Malpighian tubules, by 
means of which it finds its way into the stercoral pocket (fig. 5). 
The evidence for this somewhat remarkable conclusion will be found 
in what follows. 
On opening the body of many spiders, e. g. the common garden 
spider, Epeira diadema, the whole abdominal portion of the alimentary 
canal, with its ramifying tubules, has a very striking chalky look. In 
Epeira , the chalk-white shines through those parts of the skin which 
are free from pigment and gives rise to the white cross and spots 
which characterize it. Many observers have noticed that this chalky 
appearance in spiders is due to a layer of fine particles often showing 
a metallic glitter. There have been many conjectures as to what 
these particles are. The last conclusion arrived at (by Bertkau) is 
that the bodies strongly resemble certain constituents of the faeces 
* “Etudes sur rAnatomie de l’Epeire,” Ann. Sci. Nat., xvii. (1884). 
