286 W. F. R. WELDON. 



surface of the bladder, which stain more deeply, and are more 

 crowded with granules. The nuclei of these cells exhibit 

 frequent indications of division. 



The end-sac is by this time more closely applied to the 

 bladder, the wall of which it invaginates to such an extent 

 that about half its surface is invested by a layer of bladder- 

 cells. The epithelium of the end-sac is made up on the side 

 next the bladder of small cubical cells, and on the opposite 

 side of cells which are somewhat flattened. The protoplasm 

 of all these cells is pale and coarsely granular, as it remains 

 throughout life. The connective tissue, which was noticed in 

 the last stage, has slightly increased in amount, and the blood- 

 spaces between end- sac and bladder are much better developed 

 than during the " Mysis " stage. The renal tubule has 

 ceased to be distinguishable as a separate region, and the end-sac 

 now opens by its posterior extremity directly into the bladder. 



The stages in the further development of the bladder I have 

 been unable to observe, my remaining material consisting 

 entirely of adult individuals. It is evident, however, that the 

 end-sac becomes completely surrounded by the wall of the 

 bladder, so that it finally projects freely into the cavity of 

 that organ, being attached to the bladder-wall by a narrow 

 stalk, on which is situated the communication between the 

 cavities of the two structures. 



While the process of enclosure of the end-sac by the bladder 

 is going on, the wall of the first-named organ becomes pro- 

 duced into a number of complicated branched papillae, which 

 project into the cavity of the bladder, each being, of course, 

 covered by a layer of bladder epithelium. At the same time 

 the whole organ increases in size till it becomes about as large 

 as the whole '' green gland ^^ of False mo n. 



A section through the adult end-sac is drawn in fig. 7, 

 where the extent of the papilliform prolongations into which 

 it is produced is rather below the average. The epithelium is 

 flattened and irregular, composed of a pale, granular proto- 

 plasm. The cells do not exhibit vacuoles, and I have not 

 observed the presence of concretions in any of my specimens. 



