482 



Mr. G. H. Grosvenor. 



[Nov. 3, 



the structure and development of the individual cnidocysts have, of 

 course, been from the generally accepted point of view, i.e., that they 

 are nematocyst-secreting cells, instead of receptacles for fully formed 

 foreign nematocysts. 



The embryonic tissue of the cnidosac lies at the base, immediately 

 surrounding the opening of the ciliated canal, and differentiation 

 proceeds regularly from this point upwards, the oldest cnidocysts 

 being next the external aperture. I have never observed a layer of 

 embryonic cnidoblasts external to the fully formed ones. 



From this embryonic zone, besides the cnidoblasts or central cells of 

 each cnidocyst, there are developed certain interstitial cells which 



FIG. 12. 



-Cm. 



apparently take part in the secretion of the membranous cysts ; these 

 are perhaps what Herdman describes as young cnidoblasts. They lie at 

 first between the bases of the cnidoblasts, from which they can be 

 readily distinguished by their smaller size, and by the different staining 

 reactions of their nuclei (fig. 12). 



It is round this basal end of each cnidoblast that the membranous 

 cyst is first secreted ; the cnidoblast itself is drawn away from this point 

 towards the lumen of the cnidosac, and does not apparently take part 

 in the secretion of the cyst, but in the meantime ingests nematocysts 

 at its opposite end, which remains naked and amoeboid. When sufficient 

 nematocysts have been ingested and arranged by the cnidoblast, the 

 membranous cyst is completed, the nuclei of the intermediate cells 

 moving up between the cnidoblasts about half way towards the lumen 



