238 EEPOiiT— 1880. 



tacea presents differences in its arrangement and form from that of the 

 perfect individual, and the development of each of the medullary nuclei 

 which constitute the ganglionic masses is in relation to the development 

 of the organs to which these nuclei correspond. 



Herr C. E. Wassiliew ' has given an account of his investigations of 

 the curious ' green gland ' of the crayfish. He states that it consists of a 

 single unbroken coiled tube, closed at one end and opening at the other 

 into the sac of the gland or urinary bladder, and consists of three distinct 

 portions. The first of these has the form of a somewhat triangular yel- 

 lowish-brown lobule, lying at the upper surface of the gland and forming 

 the blind terminal portion of the whole tube ; the second forms a green 

 cake-shaped mass, constituting the lateral and inferior parts of the gland ; 

 while the third is a long, white, coiled tube, connected a.t the end with 

 the green portion and by the other opening into the bladder. 



The entire tubular gland is lined by a single layer of epithelial cells, 

 outside which is a fine structureless tunica propria, containing strongly 

 refracting nuclei. There is no cuticular lining to the tube, which thus 

 differs very markedly from the malpighian vessels of insects. 



In the yellow portion the cells are sharply defined and convex on 

 their inner surface. In the green part of the tube the cells are large, and 

 their protoplasm is in connection with a peculiar network of pseudopo- 

 deal processes which extend into projections of the wall into the lumen 

 of the tube. In the proximal portion (that nearest to the green section) 

 of the white part of the tube the walls are smooth, and lined by small 

 cells approximating the pavement form. In its distal portion mammili- 

 form and dendritic processes of the wall project into the cavity, often 

 giving the tube a spongy appearance, and the cells have long bi'oad pro- 

 cesses developed from their inner surfaces. The epithelium of the bladder 

 agrees with that of the smooth portion of the tube. 



The products of secretion are seen in the white and green, but not in 

 the yellow portion of the gland, as yellowish, rather highly refracting, 

 drops on the surface of the cells. Probably the yellow part seci'etes 

 a substance soluble in alcohol. That part of the white tube, with the 

 tesselated epithelium, most likely acts mei'cly as a duct. 



The anterior portion of the gland and bladder are supplied by a branch 

 of the antennary arteries, their posterior portions by the sternal arteries ; 

 these break up into a rich network of capillaries in all parts of the gland. 

 The nerve-supply of the bladder is also derived from two sources, its an- 

 terior part being supplied by a branch of antennary nerves (coming from 

 the supra-cesophageal ganglion), its posterior part by a nerve from the 

 supra- oesophageal ganglion, but no nerves have been observed in the 

 gland itself. 



This same green gland has been studied by Professor Huxley and Mr. 

 Martin, who, in an elementary woi'k on practical biology, describes it as 

 a soft greenish mass lying on each side of the extreme front part of the 

 cephalon, and that a fine bristle may be passed in through an aperture 

 on the first joint of the antenna?. And in his more recent work on the 

 crayfish. Professor Huxley accepts, with apparently little doubt, that the 

 green gland is the representative of the kidney. ' The green gland,' he 

 writes, ' is said to contain a substance termed guanin (so named because 

 it is found in the guano, which is the accumulated excrement of birds), 



' Zool. Atueigcr, 1, 1878. 



