2/2 PHYSIOLOGY OF THE INVERTEBRATA. 



But there is no doubt that in other forms of the lower 

 orders of the Crustacea the secretion of the shell-gland does ' 

 contain uric acid, proving the renal function of the organ in 

 question. 



In the Decapod Crtistacea * the excretory organs are re- 

 presented by the so-called green glands. Dr. Eawitz has 

 recently examined the anatomical structure of these glands 

 in Astacus fluviatilis, and his results may be summarised as 

 follows : — The gland is uniformly green on the ventral side, 

 but on the dorsal side only at the periphery ; elsewhere white, 

 with a round yellow-brown speck in the centre. When 

 examined microscopically the gland is seen to consist of two 

 tubules closely interwoven. The cells of the green part 

 contain a round grass-green drop of protoplasm, and the 



yellow-brown cells a uniformly 

 yellow-brown coloured nucleus. 

 The tubules anastomose, the 

 yellow-brown cells being the 

 c*—^ """i^SS^ terminal portions of tubules 



^'°" ^^' and secretory.f 

 Green Gland of Astacus. _i , t j. i t 

 a = glandular portion. I, = sac- ^he author % has made a corn- 

 like portion. c = opening of plete study of the fuHctiou of 



duct. d = nerve with ramifi- ^^^ gveeiL glands of AstOCllS 



fluviatilis, and the results of 

 these researches may be stated as follows: — ^The so-called 

 green glands of the fresh-water crayfish lie in the cavity of 

 the head below the front ,part of the cardiac division of the 

 stomach (see Fig. 13). The openings of these organs are 

 situated at the base of each antenna. The organ, carefully 

 dissected out of the head of a fresh-kiUed crayfish, is seen to 

 consist of two principal parts (Fig. 5 3) : a dorsal or upper- 



* The Decapoda includes the Bracliyura and the Macroma. 



t See Dr. Eawitz's paper, read before the Berlin Physiological Society on 

 January 28, 1887. 



t Dr. Griflaths' paper in Proceedings of Royal Society of London, vol. 38 

 (1885), p. 187. 



