Chap, vii.] CRUSTACEA. 253 



ascribed to the so-called "shell gland" which forms 

 a looped organ in the dorsal middle line } but there 

 are as yet no physiological facts which confirm this 

 supposition. In the higher Crustacea, an organ 

 which, in its essential relations, calls forcibly to mind 

 the arrangement of the nephridia of the earthworm, 

 is found at the base of the second pair of antennae. 

 This is the so-called " green gland " of the cray- 

 fish, where it presents the following characters. 



An orifice, large enough to admit a fairly stout 

 bristle, leads by a short canal into a wider sac, with 

 very delicate walls, which lies in front of arid below 

 the anterior portion of the stomach. Below this wide 

 thin-walled sac lies a smaller body, which is in com- 

 munication with it by a narrow coiled passage ; this 

 body consists of a yellowish-brown anterior portion, 

 which ends blindly, and of a green portion, which 

 lies between it and the duct. The former is spongy 

 in character at its anterior end, and the rest has a 

 number of lamelliform processes rising up from its 

 floor ; the green part, which is broader and natter, 

 has its walls produced into a number of small saccular 

 outgrowths. Ou the inner surface of the cells of this 

 green part, and of the succeeding white coiled tube, 

 small highly refractive bodies are to be observed, 

 which are no doubt of an excretory nature. The 

 blood-vessels which bring to the gland the materials 

 that are to be excreted by it arise from the antennary 

 and sternal arteries, and break up into fine capillaries 

 in the walls of the gland. The products excreted 

 are stated to resemble guanin, but it will be understood 

 that the small quantities which can be collected make 

 any chemical investigation a matter of considerable 

 difficulty; 



Wassiliew, to whom we owe the latest description 

 of the green gland, believes that three stages may be 

 recognised in the differentiation of the renal orgari of 



