PHYSIOLOGY OF THE INVERTEBRATA. 275 



The secretion of the green gland oiAstacus contains guanin, 

 which is proved by treating the secretion with boiling hydro- 

 chloric acid. A solution is obtained containing flakes of uric 

 acid in suspension, these are filtered ofE, and the filtrate set 

 aside to cool, when a few crystals (guanin hydrochlorate) 

 separate which are soluble in hot water. On the addition of 

 ammonia to this hot aqueous solution a precipitate is obtained 

 of guanin (C5H5N5O), the precipitated guanin being composed 

 of a number of minute microscopic crystals. On running in 

 warm dilute nitric acid (on to the slide), these crystals dis- 

 appeared, but they where precipitated again on the addition 

 of a drop of silver nitrate in the form of the nitrate of silver 

 compound (OsH.NjOjAgNOj) of guanin. 



This investigation proves that the so-called green gland 

 of Astacus fluvicdilis is a true -urinary organ, its secretion 

 containing uric acid and traces of the .base guanin. The 

 green gland is, therefore, physiologically the kidney of the 

 animal.* 



The nerve, which comes ofE from the supra-cesophageal gan- 

 glion, passes to the neck of this gland (see Figs. 13 and 53), 

 and ramifies over its surface between the outer and inner 

 membranes of which it is composed. 



In the Edriophthalmic Crustacea, there are occasionally 

 present one or two tubules which open into the posterior 

 part of the alimentary canal. These are renal organs and 

 contain uric acid. They are analogous to the Malpighian 

 tubules of the Inseda. In this respect the AmpMpoda and 

 Isopoda differ from other Crustacea. 



The Brachiopoda. 



The shell of these animals is " a cuticular structure secreted 

 by the ectoderm, and consists of a membranous basis, hardened 



* For further details see Dr. Griffiths' papers in Proceedings of Boyal 

 Society, vol. 38, p. 187 ; Chemical News, vol. 51, p. 121 ; Journal of Chemical 

 Society, 1885, p. 680 ; Science Oossip, 1886, p. 57. 



