282 W. F. R. WELDON. 



the three genera is there any connection between the wall of 

 the nephro-peritoueal sacs and the generative glands. 



The structure of the " green gland " differs in each of the 

 three genera. 



In Virbius (varians) a horizontal section through the 

 bladder and '' green gland " has the appearance represented in 

 fig. 4. The bladder itself is bounded by a single layer of 

 epithelial cells, whose inner margins frequently project irre- 

 gularly into the cavity of the organ. These cells exhibit, 

 especially in their peripheral portions, the well-marked longi- 

 tudinal striation which is so constantly noticed in excretory 

 tissues ; their internal portions are, however, frequently vacuo- 

 lated, and their free internal borders are ragged and indefinite. 

 When this condition prevails the cavity of the bladder is seen 

 (in stained sections) to contain an irregular, granular coagulum, 

 which absorbs hsematoxylin with readiness. The nuclei of 

 the bladder-cells are oval, and of moderate size; they stain 

 deeply, and do not, in preparations preserved in corrosive sub- 

 limate, exhibit any very evident reticulum. The cells com- 

 posing that portion of the wall of the bladder which invests 

 the end-sac are flatter and more regular than the others ; they 

 stain more deeply with hsematoxylin, and the longitudinal 

 striation is perhaps more evident in these than in the other 

 bladder-cells. 



The renal tubule is single, and has a much wider lumen 

 than any of the corresponding tubules of Palaemon. It leaves 

 the bladder at the postero-external margin of that organ, and 

 is at first directed nearly horizontally outwards. After passing 

 outwards for a very short distance, however, the tubule turns 

 backwards and then inwards, so that it becomes U-shaped, and 

 opens into the end-sac. The general direction of the single 

 renal tube is that just described, but it does not lie in one 

 plane with such accuracy as to enable it to be included in a 

 single section. In the section figured (PI. XXI, fig. 4) the 

 two ends of the tube only are seen, the one leaving the 

 bladder, the other entering the end-sac. By examination of 

 the following sections, the course of the tube was determined 



