MINUTE ANATOWT OF LTMNOCODIUM. 545 



very small and cubical cells which coat the subumbrellar wall 

 of the stomach. Similar cells are found lining the radial 

 canals and part of the circular canal. The genital sacs are 

 lined with a taller epithelium, a description of which is given 

 below. 



The circular canal is lined with a low epithelium, similar to 

 the one lining the radial canals, except on the outer side. 

 There, between the point of attachment of the velum and the 

 origin of the tentacles, all round the inside of the thickened 

 patch of ectoderm which forms the nettle-ring, the cells of the 

 circular canal become much thicker, and in some places the 

 cell outlines are not well defined (PI. 40, fig. 2, end.). The 

 function of the modified cells is not at all clear at present ; 

 but it is noteworthy that in Limnocnida a modified mass of 

 cells occurs in exactly the same position, but is very much 

 more largely developed. 



Reproductive Organs. — As the material at my disposal 

 consisted solely of male individuals in various stages of 

 inaturity, I have not been able to examine any females. 



The reproductive organs in the male consist of four sac- like 

 outgrowths on the subumbrellar aspect of the four radial 

 canals. The distal walls of these sacs are very thick, being 

 chiefly composed of testicular tissue, as shown in section (PI. 40, 

 fig. 7). The lumen of each of the sacs is a ventral diverti- 

 culum of the lumen of the radial canal, and is lined by a con- 

 tinuation of the endoderm of the radial canal. The cells of 

 this endodermal lining of the gonads are columnar, and rather 

 taller than the cells of the ordinary epithelium of the radial 

 canal. The nucleus of each cell is roundish, with a well- 

 marked nucleolus, and is situated near the base of the cell. 

 The protoplasm is highly granular, and near the free margin 

 of many of the cells it contains an ovoid mass which stains 

 deeply, and is probably the product of some secretory activity 

 of the cell (PL 40, fig. 8, end.). 



The mesogloea is exceedingly reduced where the testicular 

 tissue is thickest, but it is fairly well developed all round the 

 stalk of the sac (fig. 7, m. s.), to which it imparts some rigidity. 



VOL. 35, PART 4. NEW SER. P P 



