T 8 EDGAR DAVIDSON CONGDON. 



The structure seems to have arisen through the mesoglcea in 

 some way becoming attached to the perisarc without destroying 

 the continuity of the cuticular border of the ectoderm cells. 

 This could most easily take place during some time of expan- 

 sion of the ccenosarc while the perisarc and mesoglcea were near 

 each other. When contraction occurs for any reason, such as 

 the killing of the tissue, the ectoderm would be drawn tensely up 

 around the mesoglceal connective by the cuticular film. 



FIG. 7. 



Weismann found a very similar or perhaps an identical condi- 

 tion in a species of Endcndnnm. He says he found the ccenosarc 

 near the band pulled out to form a pocket to the enteric cavity 

 lined with glandular cells differing from the entoderm and form- 

 ing a secretory organ. He does not describe a pulling out of 

 the ectoderm to the point of attachment of band and perisarc. 



I found a pocket in the enteric cavity resulting from the con- 

 traction of the ccenosarc. It seems to be a mechanical necessity 

 that one be formed in the region held close to the perisarc by 

 the band. When the ccenosarc is expanded there is no pocket. 

 A few gland cells occur in the pocket but no more than else- 

 where in the entoderm. It is plain that there is not a distinct 

 glandular organ here and I doubt whether the structure is other 

 than incidental. In the expansion and contraction of the cceno- 

 sarc it seems reasonable that the apparently viscid mesoglcea 

 should become attached to the perisarc, especially in places 

 where the entoderm has more or less deteriorated. 



