PHYSIOLOGY OF THE INVERTEBRATA. 271 



The uric acid was extracted by both of the methods used 

 for testing the pyloric sacs of Uraster (see p.) 254. 



The uric acid is present as sodium urate, for sodium is 

 easily detected in the secretions of these organs. No doubt 

 some sodium compound is a normal constituent of the blood 

 of Tegenaria. 



No urea, guanin, or calcium phosphate could be de- 

 tected in the secretion. But it may be stated that 

 Dr. 0. Weinland* has recently extracted crystals of guanin 

 from the excrements of certain spiders. .The guanin so 

 extracted is stated to have answered to all the reactions of 

 that substance as described by Capranica.f 



There is no doubt that the Malpighian tubules of the 

 Arachnida are renal in function. 



The Crustacea. 



Among the lower Gni^tacea the renal organ is represented 

 by the so-called shell-gland. It consists of a coiled tube 

 with clear contents. In Apus (belonging to the Phyllopoda) 

 this gland opens by a duct " on the base of the first pair 

 of thoracic appendages, immediately behind the second 

 maxillae." 



In his paper on Cydestheria hislopiX Dr. G. 0. Sars says 

 that the only organ to which an excretory function has been 

 attributed is the so-called shell-gland (see Fig. 11). Its 

 structure is glandular, but of what nature the secretion is, 

 and in what manner performed in this species, has not yet 

 been satisfactorily ascertained. Some naturalists state that 

 this peculiar organ secretes the material of which the shell is 

 built up, but it is far from evident that such is its real 

 function. On examining the organ, Dr. Sars failed to detect 

 in this species any secreting orifice, the whole organ appear- 

 ing to constitute a convoluted canal or duct recurring in itself. 



* Zeitschrift fur Biohgie, vol. 25, p. 390. 



t Zeitschrift fiir Physiologische CJiemie, vol. 4, p. 233. 



J Christiania Videnskabs-Selslcdbs Forhandlinger, 1887, p 43. 



