274 PHYSIOLOGY OF THE INVERTEBRATA. 



most one which is a transparent and delicate sac-like body 

 filled with a clear fluid, and a ventral or an underlying 

 portion of a green colour, glandular in appearance, containing 

 granular cells. 



As is well known, these green glands were formerly 

 believed to be the auditory organs of Astacus; but in 1848 

 Drs. Will and Gorup-Besanez* stated that this organ probaily 

 contained guanin, and from this supposition the green glands 

 have been considered as excretory organs. 



The secretion of these glands is acid to litmus paper, and 

 on treating the secretions, obtained from a large number of 

 green glands, with hot dilute sodium hydroxide solution, and 

 then adding hydrochloric acid, a slight flaky precipitate was 

 obtained, and on examining these flakes under the microscope 

 they were seen to consist of small crystals in rhombic plates. 

 On treating the secretion with alcohol these rhombic crystals 

 (Fig. 54 A) were deposited; they were soluble in boiling 

 water. 



When these crystals were moistened with dilute nitric 

 acid, alloxanthine (GJH^Nfi,) was produced, and on heating 

 this substance with ammonia, reddish-purple murexide 

 (Fig. 54 B) or the " ammonium purpurate " [08H/NH4)N505] 

 of Prout was obtained. The murexide so obtained crystallises 

 in prisms, which by reflected light exhibit a splendid green 

 metallic lustre, and by transmitted light are a deep reddish- 

 purple. On running in a solution of potassium hydroxide 

 upon a microscopic slide containing some of the murexide 

 crystals they were dissolved. 



It is evident (from the above reactions) that these rhombic 

 crystals are deposits of uric acid (GJl^fi^) from the secretion 

 of the green gland of the crayflsh. These deposits of uric 

 acid crystals were covered more or less with a very thin and 

 superflcial coating of some brown colouring matter, probably 

 one of the pigments already described, 



* See Munchen Gelehrle Anzeigen, No. 233, 1848. 



