196 THE BIOLOGY OF HYDRA : 1961 



information will be added as we gather more information on fine 

 structure and as further chemical and biochemical studies are car- 

 ried out. One could suggest from observations on available elec- 

 tron micrographs such as those of Yanagita and Wada (11), Chap- 

 man and Tilney (4) and unpublished ones of Miss Westfall's that 

 the shaft of some heteronemes is folded accordion style. If to this 

 we add the fact that the capsule contracts on explosion, we could 

 imagine that the shaft of these nematocysts unfolds as it everts. 

 This may account for the full eversion of heavily armed shafts and 

 only later would uptake of water play a role in eversion. This sug- 

 gestion can be at least partly tested by critical analysis of the length 

 of the sculptured or folded outline of uneverted shafts as com- 

 pared with the full length of everted ones. 



It is a rare field of biology where one can say the last word has 

 been said and one wonders if such a field exists, but the study of 

 nematocysts seems clearly to be in its infancy and there is little 

 chance of running out of problems ( or words ) . I do feel, however, 

 that with the renewed interest in these intriguing and complicated 

 structures which has appeared in recent years there is high hope 

 that many of our problems will be solved. I look forward with ex- 

 citement to the time in the future when we have enough knowl- 

 edge to talk about the types, structure and function of nematocysts 

 rather than what is not known. 



REFERENCES 



1. Burnett, A. L., T. Lentz and M. Warren, 1960. The nematocysts of hydra 



( Part I ) . The question of control of nematocyst discharge reaction by 

 fully fed hydra. Ann. Soc. Royal Zool. Belgique 90: 247-267. 



2. Carlgren, O. 1940. A contribution to the knowledge of structure and distribu- 



tion of cnidae in the Anthozoa. Kungl. Ftjmig. Sdllskapets Handl. N. F. 51 : 

 1-62. 



3. Chapman, G. B. and L. G. Tilney, 1959. Cytological studies of the nemato- 



cysts of Hydra. I. Desmonemes, isorhizas, cnidocils, and supporting struc- 

 tures. /. Biophijsic. and Biochem. Cijtol. .5: 69-78. 



4. Chapman, G. B. and L. G. Tilney, 1959. Cytological studies of the nemato- 



cysts of Hydra. II. The Stenoteles. /. Biophysic. and Biochem. Cytol. 

 5: 79-84. 



5. Cutress, C. 1955. An interpretation of the structure and distribution of cnidae 



in the Anthozoa. Systematic Zoology 4: 120-137. 



