450 W. DE MORGAN AND THE LATE G. HAROLD DREW. 



comparatively small compared to the number seen in unfixed prepara- 

 tions. This was probably due to the fact that the endodermal cells,, 

 being kept in motion by their flagella, do not settle down on the surface 

 of the glass like the nonmotile ectoderm cells, and consequently do not 

 adhere to it on the addition of the fixative. 



Examination of these preparations (Fig. 4) showed that the ectodermal 

 cells had mostly become rounded, their nuclei were somewhat indistinct, 

 and no nuclear membrane was distinguishable. The nucleoli in some 

 cases stained darkly, and from them a few short radiating strands of 

 chromatin could often be made out, but in other cases the whole nuclear 

 structure stained faintly and appeared as a roughly spherical mass of 

 indeterminate structure. The cytoplasm of these cells was clear, the 

 periphery often staining somewhat darker than the more central part. 

 Where occurring in small aggregates, the ectodermal cells appeared 

 comparatively uninjured, and closely resembled the normal. In the 

 case of the isolated cells it would seem as though the pressure to which 

 they had been exposed had burst the nuclear membrane and caused a 

 fusion of the nucleoplasm and cytoplasm. 



The larger endodermal cells in these fixed preparations had lost their 

 columnar shape and become rounded, and their flagella were not seen. 

 The nuclei were indistinct and appeared as a light area in which a few 

 granules of chromatin could be distinguished, surrounded by the darker 

 cytoplasm. In most of the cells the cytoplasm had lost its granular and 

 vacuolated character, but in a few some darkly staining granules were 

 present. As might be expected from their larger size, the endoderm cells 

 appear to have suffered more from the squeezing process than the smaller 

 endoderm cells. 



Interspersed between the cells all over the preparations were large 

 numbers of nematocysts, many of them apparently uninjured, and 

 granules and globules derived from disintegrated cells and the contents 

 of the enteric cavities of the Hydroids. 



After squeezing through bolting silk into a watch-glass containing 

 a little water, the isolated cells, small cell aggregates, and general debris, 

 w^hich escape through the silk, soon settle down and form an even layer 

 of a greyish yellow colour over the bottom of the watch-glass. Within 

 two or three hours this layer shows a tendency to subdivide into a num- 

 ber of small nodules, and after the lapse of another hour these nodules are 

 usually distinct elevated aggregations, often connected with one another 

 by fine strands which gradually become thinner and contract until they 

 are absorbed into the nodules from which thev radiated. If left undis- 



