RENAL ORGANS OF CERTAIN DECAPOD CRUSTACEA. 289 



but the. characters of the remaining portions of the excretory 

 system vary greatly. 



In the Thalassinidse (Axius and Gebia) the number of 

 the tubules, and the complexity of their arrangement, have 

 increased, so that several tubules lead from the ureter to the 

 end-sac; but there is no vesicular dilatation of any part of 

 the system. 



In the Astacidse (Astacus, Homarus, and Nephrops) 

 several tubules run from the ureter to the end-sac ; but by the 

 dilatation of one of these, which receives the openings of the 

 others, a bladder is constituted ; and this bladder intervenes 

 between the plexus of tubules, forming the mass of the " green 

 gland," and the ureter. In this group the bladder has no 

 considerable extension into the thorax. 



In the Loricata (Palinurus) the bladder has the same 

 relations as those described in the Astacidse; but the 

 number and complexity of the tubules forming the green 

 gland is very largely increased. 



In the Carididse the structure of the excretory system 

 varies greatly, the four modifications described in the previous 

 section of this paper all occurring within the limits of the 

 group. 



In the "Anomura" there is a well-marked nephro- 

 peritoneal system, which in Pagurus forms a median dorsal 

 sac, situated far back in the abdomen. The end-sac is fre- 

 quently produced into papillae, which are surrounded, not 

 by a modified portion of the bladder, as in Pandalus and 

 Crangon, but by a layer of renal tubules. 



In the Brachyura the nephro-peritoneal sac sends well- 

 developed prolongations into the thorax ; there are, at least 

 frequently, two such prolongations on each side, one dorsal 

 and one ventral. The end-sac is frequently produced into 

 papillae, which are covered by the epithelium of the short, 

 wide renal tubule, the cavity of this tubule being frequently 

 broken up by a system of trabeculse.^ 



• 111 this sketch of the various Decapods, the account of the Thalassinidse 

 and of tlie Brachyura is taken directly from Marchal's paper. 



