238 JAMES ERNEST KINDRED. 



is a thin layer of syncytial reticular connective tissue (pr.} which 

 is directly continuous on its inner surface with the definitive 

 stereom (s/.). This syncytium is loosely organized and has 

 large intersyncytial spaces within which are found wandering 

 " amcebocytes with spherules. " The cytoplasm of the syncytium 

 is fibrous in appearance and the remnants of spicules could be 

 observed in it. The traces of spicules were more marked in the 

 region bordering on the stereom where the syncytium had the 

 trabecular organization characteristic of the stereom. This 

 region I have designated as the prestereomal area. The stereom 

 is made up of I-shaped trabeculse which are apparently joined to 

 each other end to end, so that the whole stereom is a framework of 

 beams and rafters with regular lacunar spaces. The substance 

 of the stereom when observed in the unstained condition is clear 

 crystalline in character and when stained is intensely basophilic 

 in reaction. A prestereomal area is also found between the 

 stereom and the peritoneum. From the organization and rela- 

 tion of the prestereomal areas to the stereom it is evident that the 

 growth of the stereom takes place peripherally by the gradual 

 deposition of skeletal material within the prestereomal trabeculae. 

 Nuclei with prominent nucleoli were observed in the prestereomal 

 trabeculae, but none were observed in the trabeculse of the ster- 

 eom. This condition would indicate that trophic activity of the 

 cells is lost in giving rise to the stereom and that the whole cyto- 

 plasm of the syncytium becomes converted over into skeletal 

 material while the nucleus degenerates. Now if a cut were made 

 directly through the body wall and a piece of it removed, the cut 

 surface would present three regions, a middle stereom region and 

 two peripheral prestereomal areas. It is obvious that the pre- 

 stereomal areas would be capable of replacing certain parts of the 

 test, but the question arises as to whether or not these cells are 

 aided in this regeneration by the leucocytes. 



Although the body wall of several specimens of S. drobachiensis 

 were resected in an attempt to answer this question, the results 

 are far from convincing and the description. of the regeneration of 

 the test which follows is to be studied more in detail at a later 

 date. 



Eight specimens of S. drobachiensis were injected with carmine 

 in seawater through a minute perforation in the peristomial mem- 



