EENAL ORGANS OP OEETAIN DECAPOD CRUSTACEA. 283 



as that shown by the dotted lines in the figure. [The deter- 

 mination of such a point is so easy that it has not seemed 

 worth while to publish the figures of the sections upon which 

 it rests.] 



It is evident that the single, wide, U-shaped tube, running 

 from the bladder to the end-sac, is the only representative in 

 Virbius of the complicated plexus which goes to make up the 

 mass of the green gland in the Prawn. In structure, its walls 

 somewhat resemble those of the bladder already described. 

 They are, however, higher and more regular, their internal 

 extremities of the component cells being less given to the 

 exhibition of vacuoles and irregular processes. The longi- 

 tudinal striation is more evident, and the nuclei are larger 

 and stain more deeply with hsematoxylin. Before opening 

 into the end-sac, the lumen of the renal tubule contracts con- 

 siderably, so that the orifice, by which the cavities of the two 

 structures communicate, is very small. Owing to its size and 

 position, it is exceedingly difficult to demonstrate this opening 

 in transverse sections, but in carefully adjusted horizontal 

 longitudinal sections it is, as will be evident from the figure, 

 easily to be seen. 



The end-sac itself is completely enveloped by a layer of 

 bladder epithelium, the wall of the bladder being invaginated 

 by it. The epithelium of the bladder is, however, not in 

 absolute contact with that of the end-sac, the two being sepa- 

 rated by a blood-space (left white in the figure). I have not 

 been able to detect any epithelium bounding this blood-space ; 

 and I am inclined to believe, after careful examination, that 

 no such epithelium exists. The account given by Grobben of 

 the end-sac of Palsemon treillianus leads to the belief 

 that the renal vessels of this species end in lacunje which are 

 devoid of epithelial lining ; and I have been unable to demon- 

 strate an epithelium in the smaller blood-spaces of the kidney 

 ofPandalus (annulicornis and brevirostris). Professors 

 Claus^ and Lankester^ have, as is well known, arrived inde- 



» « Arb. Zool. lust. Wien,' Bd. v, Heft 3 (1884). 

 ^ This Journal, vol. xxv, p. 518. 



