PLATE XXVIII 



Fig. i. Gas-gland ectoderm from a young Physalia. The nuclei only 

 are stained (Helly, Feulgen). 



Fig. 2. Gas-gland ectoderm from another specimen, showing an 'islet' 

 of six cells. The dark dots in the surrounding tissue are the nucleoli 

 of the columnar cells. Some exceptionally large nucleoli to the 

 right of the 'islet' belong to polyploid cells (F.W.A., iron haemat- 

 oxylin). 



Fig. 3. A pair of young cnidoblasts from the ectoderm of a gastrozooid, 

 showing Hirschler's 'fusom' (Ca-formaldehyde, silver). 



Fig. 4. A group of four prematurely discharged developing nematocysts 

 from a gastrozooid. The cnidoblasts are not stained (formaldehyde- 

 sublimate, silver). 



Fig. 5. Part of the incompletely discharged filament of a large isorhiza. 

 The undischarged part is seen coiled within the discharged part 

 (phase contrast). 



Fig. 6. Group of large isorhizas from a tentacle. The arrow indicates 

 part of a discharged filament showing the three spiral ridges beset 

 with teeth (phase contrast). 



Fig. 7. Fibrillar 'basket' from a cnidoblast, isolated by peptic digestion. 

 The nematocyst (a large isorhiza) has escaped from the 'basket' 

 leaving it somewhat distorted. The reticular association of fine 

 fibrils around the apical opening is shown (phase contrast). 



