216 K. Ogumu: 



cuticular coveriiig distiiictly visible at the outeriiiost surfacc wherc Ihc 

 water of the exterior comes in direct contact, and it is probable that, 

 when the earlier ecdysis takes place, this covering is cast off from the 

 cell and remains in the exuviae. Such being the striicture, the cells of 

 the cushion remind iis of those of the glandulär epitheluni in the other part 

 of the alimentary canal. The boundaries of each cell are not so indistinct 

 as Sadoncs says, especially on a tangential section (fig. 6). Besides the 

 normal series of nuclei, near the basenient menibrane, there may often be 

 observed a few different nnclei in the cushion a few nuclei of smaller size 

 which were called the accessory cells by Sadones, who did not give 

 accurate demonstration of their destination or nature. Lastly, a thin 

 menibrane (fig. 4 bm) lining the inner surface of the cushion is, I as 

 think, not other than the basement menibrane which was overloked by 

 Sadones. This menibrane has a peculiar function in the next period of 

 growth. as mentioned elsewhere. To summarize the obove accounts 

 adverse to those Sadones says on the structure of cushion cells: 

 In his niaterial, L. depressu, (li the elongated nuclei are laid without 

 exception, perpendicular to the cushion surface, while in my material 

 L. 4-maciilata — they otherwise lie as alreay noted ; i2i the concentric 

 arrangement of the cells is not the case, while it is obvious in my niaterials; 

 (3) the trabecular structure of the cell contents which is emphasized by 

 him is in fact the feature which is common to all glandulär epithelium 

 of alimentary canal ; and (4) the presence of the basenient menibrane, on 

 which says nothing. 



It is also noteworthy that the cuticula of the cushion is thin and 

 is in very close contact with cells, while in other parts of the gill its 

 attachment is so loose as to be seen separated entircly from the gills in 

 prepared specimens. 



Muscies and Tracheal Branches in the Rectum. 



The rectum is provided with two kinds of muscie layers in its 

 wall. One of these, the circular muscie layer, consists of striped fibres 

 running around the rectum, and the other situated superficially to the 

 last layer is separated into six distinct bundles of muscie fibres, which are 

 distributed on six lines where every two of the double gill rows come 

 in contact to each other. 



Each three of six double rows of gills Stands separated by the 

 dorsoventral sagittal plane of the rectum. The tracheal branches enter 

 into each half in such a way that those from the dorsal trunk cnler the 

 iipper and niiddle rows, while those from the visceral trunk go into the 

 lamellae which constitute the ventral row of gills. These tracheal branches, 

 after entering the lamellae, raniify into smaller branches successively, 

 until they are divided at last into the finest anastomose. 



