Digestive Processes in Arachnids. By H. M. Bernard. 437 
evidence of sucli an interpretation, while on the other hand there is a 
certain amount of evidence in favour of the view put forward in this 
paper. We have, further, some indirect evidence against the supposi- 
tion that this peritoneal faecal matter results from normal waste. 
Garrod’s * researches tend to show, in Vertebrates at least, that urates 
in the blood and tissues are derived either directly from the food, if it 
happens to contain urea, or by absorption from the kidneys where it 
is normally formed. Assuming that the same law applies to the 
Arachnida, it is hardly likely that these crystal-like masses in the 
peritoneal cells of spiders are due to the presence of uric acid in their 
food, as we find no trace of such substance in the peritoneal cells of 
the Chernetidas and Galeodidae, whose food very much resembles that 
of the Spiders.! Further, I think it highly improbable that this 
substance is formed in the cells of the Malpighian tubules partly to 
be discharged into the stercoral pocket, and partly to be absorbed by 
the surrounding tissues. The Malpighian tubules, of no other Arach- 
nids, produce such bodies. Plateau distinctly calls attention to the 
fact that there is “ no guanin in the products of the Malpighian 
tubules of Phalangids, so characteristic of the urinary secretions of 
Araneids.” | The Malpighian tubules of Euscorjpio and of Galeodes 
are searched in vain for any such substance, while Obisium has no 
Malpighian tubules. 
Again, the arrangement of the Malpighian tubules in the Araneids 
seems to be unique among the Arachnids. Instead of being bathed 
by the body fluid, they form, with the peritoneal cells and the 
digesting tubules, a compact mass. In fig. 5, and again even more clearly 
in Bertkau’s figure, § the Malpighian tubules are seen to be completely 
embedded in the peritoneal cells. This seems to imply a close 
physiological connection between these tubules and the peritoneal 
cells, which latter we have seen are in close physiological connection 
with the alimentary canal. Indeed, it seems to me not altogether 
improbable that in the Araneids, which are the only Arachnids 
whose spinning glands are always functional, and presumably always 
carrying away waste products, the Malpighian tubules may have 
become specialized for the purpose here described, viz. of removing 
faecal matter from the peritoneal cells. Further, a point of some 
significance deserves mention. The greater part of the chalky 
matter, in the peritoneal cells, is found at the periphery of the com- 
pact mass formed by the digesting tubules. This is where we should 
naturally expect to find it, because it is most difficult to get rid of the 
faeces from the blind ends of the tubules. The essential similarity 
between this chalky-looking matter in the peritoneal cells and the 
* “ On the Place of Origin of Uric Acid in the Animal Body,” Proc. Roy. Soc., 
xl. (1886) p. 484. 
f It deserves mentioning, however, that the food of spiders may be mixed with 
the secretions of their own poison-glands. 
X Tom. eit., p. 441 (p. 75o). § Tom. cit., p. 428 (plate xii. fig. 4). 
