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diverticula are hepatic or pancreatic glands, and the contents of 
their epithelial cells secretions. One of the more interesting facts 
recorded by Plateau relates to the detachment of a great number 
of the epithelial cells which float off into the lumen of the gut ; their 
contents, according to Plateau’s figures, are similar to those of detached 
or stationary digesting cells of other Arachnids, viz. round homo- 
geneous globules, which can hardly fail to be food-globules, and minute 
black points, which are doubtless the faecal “ crystals ” so often men- 
tioned above. It would be interesting to investigate the fate of these 
detached cells in the Phalangiidae, to see whether they offer any sup- 
port to my suggestion that in Scorpio they become blood-corpuscles. 
It should not, however, be forgotten that the Phalangiidae have a rich 
system of tracheal respiratory tubes, and that consequently the circu- 
latory blood system is not so highly developed as in Scorpio with its 
respiration localized in the lung-books. 
In both these Arachnids, Scorpio and Phalangium, I attribute 
the detaching of the cells to the fact that they are digesting cells, a 
certain number of which, when they are all distended with food- 
globules, are crowded out. The storing up of the food-globules in the 
peritoneal layer observed in Scorpio and the Araneids, may be but a 
further attempt to obtain relief from this excessive crowding of the 
distended cells. Plateau’s drawings of the peritoneal cells of Phalan- 
gium (his “ fat-body ”) seem to indicate that they are full of round 
granules which may perhaps represent stored-up food-globules. 
Acarid^i. 
I have only examined sections of Tetranychus tiliarum, which 
undoubtedly feeds on vegetable juices. Its hind-gut was full of the 
typical “ crystals ” which seem invariably to result from the assimila- 
tion of protoplasmic compounds. I could make nothing of the 
digestive cells themselves. 
I learn, however, from Mr. Michael, that it is not uncommon to 
find great accumulations of white chalky matter either being slowly 
got rid of, or else permanently located in the body-cavities of certain 
mites. That this chalky matter is similar to the chalky matter in the 
peritoneal cells of Araneids and also to a small extent in the 
peritoneal cells and blood-corpuscles of Scorpio seems to me very 
probable. Some further light is perhaps thrown on this phenomenon 
by the fact, for which I am also indebted to Mr. Michael, that the 
digesting cells in Acarines are often found detached from the epithelium. 
This suggests the overcrowding of the cells with food, and might also 
imply the storing up of food-globules in mesodermal cells, the diges- 
tion of which would account for the chalky matter. We can only hope 
that Mr. Michael will shortly publish an account of his extremely 
interesting observations on this subject. 
