EENAL ORGANS OF CERTAIN DECAPOD CRUSTACEA. 281 



peatedly described, especially by Grobben, Marchal, and 

 myself. 



In my former paper I described only the arrangement 

 found in P. serratus, and the observations of M. Marchal, 

 which are in complete agreement with my own, relate also 

 to this species. I have since satisfied myself that the ex- 

 cretory system of P. squill a, and that of Palsemonetes 

 varians, are practically identical with that of the species 

 described. 



In the genera Virbius, Pandalus, and Crangon, a 

 series of modifications may be observed, resulting in the dis- 

 appearance of the whole tubular portion of the green gland, 

 and the hypertrophy and specialisation of the end-sac. The 

 nephro-peritoneal sacs are also arranged in a manner strikingly 

 different from that which obtains in the Prawns. 



The nephro-peritoneal sacs are nearly identical in 

 arrangement in the three genera in question. Their relations 

 will be readily understood from the diagram, fig. 10, and the 

 transverse section of Pandalus brevirostris, fig. 3. The 

 bladder gives off from its internal aspect a duct, which is both 

 wider and shorter than the corresponding duct of Palsemon, 

 the duct from each bladder passing inwards under the 

 oesophageal commissure of its own side, and opening into a 

 large sac, which does not communicate with its fellow of the 

 opposite side, and which does not extend to the middle dorsal 

 line above the alimentary canal. The median wall of each 

 sac is closely applied partly to the lateral and ventral wall 

 of the stomach, and partly to the median face of the sac of the 

 opposite side, so that the stomach appears in section to be 

 supported by a well-marked ventral mesentery, which exists 

 beneath the part of that organ which projects in front of the 

 oesophagus, as well as beneath its post-oral region. Both 

 bladder and sac give off numerous processes, which ramify 

 in the base of the antennae and among the organs of the 

 thorax. The epithelium forming the walls of these organs is 

 in all cases striated and excretory, being very closely similar 

 to the corresponding epithelium of the Prawns. In none of 



