EENAL OEGANS OF CERTAIN DECAPOD CRUSTACEA. 287 



The nuclei are small, rounded, and pale, with scattered, deeply 

 staining chromatin granules. The communication between 

 the cavity of the organ and that of the bladder is seen to lie 

 at one side of the stalk, and to be quite direct, without the 

 intervention of anything which can be held to represent the 

 system of tubules of Palsemon, or even the simple Jj-shaped 

 tubule of Virbius. 



Between the wall of the end-sac and the investing portion 

 of the bladder there is a certain quantity of connective tissue, 

 which in places forms fairly conspicuous masses, the characters 

 of which tissue will be gathered from the figure. Besides 

 the connective tissue a system of blood-vessels ramifies between 

 end-sac and bladder, consisting in part of larger vessels, in 

 which it is easy to recognise an epithelial lining, and in part 

 of smaller, apparently lacunar spaces. These vessels are sup- 

 plied by one or two main trunks which pass along the neck of 

 the end-sac. Two of these vessels, cut transversely before 

 their entrance into the space referred to, are seen in fig. 7 

 lying outside the wall of the bladder. 



The epithelium of the bladder itself is everywhere the same. 

 The cells are columnar, and very regular in outline, showing no 

 trace of vacuolation or of production into irregular processes. 

 They exhibit an exceedingly well-marked longitudinal striation, 

 and stain deeply both with hsematoxylin and with borax 

 carmine. The internal border of the bladder-cells seems always 

 to be darker and more homogeneous than the rest, but there 

 is no indication of the existence of a definite cuticle. The 

 nuclei are rounded and granular, and stain fairly deeply. 



The youngest individuals of Crangon vulgaris which 

 were examined had already attained the external characters of 

 the adult, although they were scarcely larger than the oldest 

 " Mysis " larvae. 



These specimens correspond in age to the second stage in 

 the development of Pandalus, as above described, and the 

 condition of the excretory system is practically identical in 

 the two species. 



The bladder- wall in the young C. vulgaris (see PI. XXI, 



