CADET HAND 197 



6. Ewer, R. F. 1947. On the functions and mode of action of the nematocysts of 



Hydra. Proc. Zool. Soc. London 117: 365-376. 



7. PiCKEN, L. E. R. 1953. A note on the nematocysts of Conjnactis viridis. Quart. 



Jour. Micros. Sci. 94: 203-227. 



8. RoBSON, E. A. 1953. Nematocysts of Corynactis: The Activity of the filament 



during discharge. Quart. Jour. Micros. Sci. 94: 229-235. 



9. Slautterback, D. L. and D. W. Fawcett, 1959. The development of the cnido- 



blasts of Hydra. An electron microscope study of cell differentiation. /. 

 Biophysic. and Biochem. Cytol. 5: 441-452. 



10. Weill, R. 1934. Contributions a I'etude des Cnidaires et de leur Nematocystes. 



Trav. Stat. Zool. d. Wimereux Tome 10, 11. Paris. 



11. Yanagita, T. M. and T. Wada, 1959. Physiological mechanism of nematocyst 



responses in sea-anenome VI. A note on the microscopical structure of 

 acontium, with special reference to the situation of cnidae within its sur- 

 face. Cytologia 24: 81-97. 



DISCUSSION 



GOREAU: To those of us who swim in reefs and sometimes 

 come into painful contact with Millepora complanata and similar 

 stinging species, it would be of interest to know what nematocysts 

 produce the burning sensation and the erythema. 



HAND: Four categories have been described: atrichs, basitrichs, 

 macrobasic mastigophores and stenoteles. One could guess that the 

 stenoteles and macrobasic mastigophores give you the kick. 



MUSCATINE: Has anyone observed the extrusion of substances 

 from the end of nematocyst threads? 



HAND: Yes, I think there is a lot of information about material 

 being extruded, and one of the places this is most readily visible 

 is in the big holotrichs that corallimorpharian anemones and some 

 corals have. First, there is an uptake of methylene blue. Then there 

 is eversion of the thread as Picken and Robson have explained so 

 beautifully. And then real droplets of the material leave the terminal 

 end of the thread. One can see this happening in a fresh prepara- 

 tion. Whether or not this is the toxin, and what relation this has to 

 the total picture, is not at aU clear. But certainly there is something 

 leaving the capsule. And the total volume of the everted system is 

 in general greater than the uneverted system. In order to create 

 this, something has had to move into the system or expand within it. 



