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Transactions of the Society. 
they are deeply stained. The faecal crystals are seen here and 
there travelling up into the lumen of the gut from between the cells. 
But by far the greater number of the crystals were massed along the 
bases of the cells, just inside the basement membrane, giving a brown 
appearance to the basal half of the digesting epithelium.* No food- 
globules could be found anywhere among the peritoneal cells. The 
Malpighian tubules, however, were full of faecal “ crystals.” Where 
did they come from ? Close examination showed them suspended 
here and there on the protoplasmic strands of the peritoneal cells, 
apparently on their way from the digesting diverticula to the 
Malpighian tubules. 
We have here, then, a case of a fasting spider with no surplus 
food-globules stored up in the peritoneal cells, and yet an immense 
number of faecal “ crystals ” in the Malpighian tubules. I can only 
suggest that these faecal “ crystals” came from the basal ends of the 
digesting cells, this being no more difficult to believe than that food- 
globules or carmine-grains pass out from the endodermal into the 
mesodermal cells. 
With regard to these two explanations of the presence of this 
guanin in the peritoneal cells, I do not see why both of them should 
not be correct. We know that bodies strongly resembling food-glo- 
bules are found in the peritoneal cells of the Spiders, and we know 
from Euscorpio that such bodies may undergo a process of digestion 
in these cells. But unless the digestion of food-globules in the peri- 
toneal cells is more frequent in the spiders than it apparently is in 
Euscorpio, it would hardly account for the enormous number of faecal 
“ crystals ” found in their peritoneal cells and Malpighian tubules. 
I therefore think that we must look for the main supply of these 
bodies to the digesting tubules themselves in the manner above 
described. I am inclined to think that a certain number of the 
faecal “ crystals ” in the digesting cells are broken down into smaller 
bodies, able to pass easily through the wall of the gut, or else that the 
smaller bodies are selected for this purpose, while the larger, or those 
not broken down, are excreted into the lumen of the gut. The bodies 
which find their way into the Malpighian tubules seem to be ground 
down to form the minute round bodies found in the stercoral pocket, 
wdiich differ from those forming the faecal masses, and which Plateau 
has traced to the Malpighian tubules. 
In putting forward this explanation of the phenomenon, I do not 
lose sight of the fact that these crystal-like bodies in the peritoneal 
cells and the Malpighian tubules of Araneids may be some form of 
normal waste product, some compound of urea, presenting a close 
resemblance to the faecal “ crystals ” which result from the digestion 
of the food-globules within the gut. So far, however, we have no 
* Cf. Bertkau’s figures (tom. cit., p. 428), where he shows the crystalline contents 
of the cells collected chiefly at their bases. 
