448 W. DE MORGAN AKD THE LATE G. HAKOLD DREW. 



The smaller ectoderm cells are slightly elongated, often with pointed 

 ends, with the exception of those forming the layer lining the hollow of 

 the canosarc, which are almost cubical in shape. The nuclei are small, 

 and the nucleoli relatively large and distinct. 



Other structures such as the germ cells, nematocysts, etc., are not 

 described here as they appear to merely play the part of foreign bodies 

 in the restitution masses, and do not enter into their development. 



THE PROCESS OF FORMATION OF RESTITUTION MASSES. 



The cells that are obtained after squeezing through bolting silk of 

 DO meshes to the inch are, many of them, comparatively little damaged ; 

 but if a finer silk is employed, such as that having 180 meshes to the inch, 

 the majority of the cells are crushed and broken. It would appear that 

 the injury caused by squeezing through a fine meshed silk is due rather 

 to the relatively greater pressure that must be applied to the bag con- 

 taining the pieces of Hydroids in order to drive the cells through the 

 fine meshes than to the actual size of the meshes themselves. Restitu- 

 tion masses that would live more than a few days, and which would show 

 any degree of subsequent development, were not obtained when a finer 

 mesh than 50 to the inch was employed, and accordingly this was most 

 generally employed. 



An examination of the cells immediately after squeezing through a 

 50-mesh silk showed that the majority of them were single and isolated 

 from their neighbours ; small cell aggregates consisting at the most of 

 six or eight ectodermal cells were present, and aggregates consisting of 

 a smaller number of endodermal cells could be seen. These endodermal- 

 cell aggregates, as well as the isolated endodermal cells, were in active 

 motion caused by the action of their flagella : in the case of the isolated 

 cells this motion consisted in progression in a number of small spirals 

 due to the fact that the flagella are only attached to one side of the cell. 



In addition to the comparatively uninjured cells and cell aggregates, 

 a good deal of granular debris was present, and minute rounded bodies 

 which were presumably small protoplasmic masses produced by the dis- 

 integration of cells which had been actually crushed in the squeezing 

 process. Many nematocysts, some with their threads ejected, could also 

 be seen, and ova were often present. In some cases small pieces of the 

 tentacles accidentally were forced through the meshes of the silk intact ; 

 but these were usually visible to the naked eye, or under a low power of 

 magnification, and when seen were removed with fine-pointed forceps. 



