272 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 Criidacca * the excretory organs are re- 

 presented by the so-called green glands. Dr. Rawitz 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 



e-s— ^.«»:.;=.^ terminal portions of tubules 



^'^^' ■S^- and secretory. t 



Green Gland of Astacus. rm ,^ J.^ t 



, ,, . , i he author! has made a com - 



a — glandular portion. /' = sac- ^ 



like portion. c = opening of plcte study of the function of 



duct. ,/ = nerve with ramifi- ^j^q green glands of Astacus 



cations. X 2 (about). /» • j •? • n j_i i. p 



jlnviatihs, and the results 01 

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

 gi'een 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-killed crayfish, is seen to 

 consist of two principal parts (Fig. 53): a, dorsal or upper- 



* The Decapoda includes the Brachytira and the Jlncroura. 



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

 January 28, 1887. 



J Dr. Griffiths' paper in Proceedings of Eoijal Society of London, vol. 38 

 (1885), p. 187. 



