THE EDWARDSIA-STAGE OF LEBRUKTA. 279 



appear in the deeper regions and as far as the mesogloea. A 

 peripheral zone of the ectoderm is nearly colourless, being con- 

 stituted mainly of the distal portions of the extremely long 

 supporting cells, unicellular glands with clear contents, and a 

 few gland-cells with fine granular contents. These last stand 

 out very distinctly in sections stained with indigo-carmine. The 

 nuclei of the principal zone are oval and closely arranged, stain- 

 ing not nearly so intensely as those of the stcimodseum and 

 mesenterial filaments. The inner nuclei are rounded and much 

 more scattered ; some approach the supporting lamella, and others 

 appear partly or even entirely included within it. The meso- 

 gloea of tlie adult polyps contains numerous isolated cells equally 

 distributed throughout, and there is little doubt that these are 

 derived both from the ectoderm and the endoderm. For in the 

 larrae nuclei in similar positions to those of the ectoderm already 

 referred to also appear on the internal side, and the thiu lamella 

 of the mesenteries also displays included cells. Both in longi- 

 tudinal and transverse sections a very delicate layer of nerve-fi.brils 

 can be distinguished next the mesoglcea, much more obvious at the 

 narrower end (PL 19. fig. 21). Maceration-preparations of such 

 delicate material in the preserved condition did not yield good 

 results, but I was able in some instances to distinguish the usual 

 nerve-fibrils of the sensory cells. 



No distinct evidence of muscular fibrils occurs on the ecto- 

 dermal side, but in longitudinal sections such can be recognized 

 on the inner border of the mesogloea of all but the youngest 

 larvse (fig. 21). 



The nematocysts are of two kinds. A long narrow form 

 extends almost across the layer and is distributed throughout 

 the ectoderm, even as far as the aboral region. They parti- 

 cularly crowd the tentacular area. On maceration, a very 

 small oval form is also obtained, often with the nucleus of 

 the cnidoblast still connected. These are not early stages of 

 the larger variety, as the developing forms of these latter are 

 very conspicuous objects. 



The large nematocysts are extremely thin-walled, nearly trans- 

 parent, and usually only a central, nearly straight, more highly 

 refractive axis can be distinguished, extending from one end to 

 near the other. In some conditions the presence of a very 

 delicate, closely spiral thread can be observed in addition. Nearly 



