CADET HAND 195 



pear that all the heteronemic stomocnidae are penetrants, but the 

 functions of most haplonemic stomocnidae are not known though 

 we may assume they are adhesive. Among the astomocnidae we 

 find the entangling desmonemes, but what of the rhopalonemes? 

 As well as being in doubt of the function of most nematocysts we 

 are again faced with diversity for which it is not easy to see adap- 

 tive values. Cleverly contrived experiments may be able to answer 

 many of these questions, but the possibility exists that nematocysts 

 may be another example of variation without functional significance. 

 At the moment it is difficult for me to imagine what functional 

 differences one could ascribe to a series of mastigophores with no 

 threads, short threads or long threads. Such variations exist, how- 

 ever, and in discrete places and patterns, that is one species 

 may have one type in one tissue, another in some other tissue, while 

 a second species will show only one type in one place. Certainly 

 types deserves attention. 



The problem of how nematocysts discharge is a complicated 

 one and one to which many authors have addressed themselves. 

 The cnidocil, which is so characteristic of at least some nemato- 

 cysts of hydra, is not known to be associated with most nemato- 

 cyst types, and in fact has been reported only in hydrozoans. When 

 and if a final relationship between cnidocil and discharge in 

 stenoteles and desmonemes is worked out we still will have to re- 

 solve the problem of how other nematocysts are related to what is 

 found here. We have seen no signs of cnidocils in Metriditim acontia. 



What the operculum is, or even if it exists in most nematocysts 

 is a difficult problem. There seems to be little doubt that some sort 

 of a plug or structure exists at the point on a capsule where the 

 thread or tube starts everting. In stenoteles the operculum is a real 

 structure as demonstrated by the electron microscope studies of 

 Chapman and Tilney (4). In Miss Westfall's studies of nemato- 

 cysts no operculum has yet been seen, although the material has 

 not made optimum observation on this point possible to date. 



The mechanism of discharge has been analyzed by many people 

 and I do not feel a detailed summary is called for here. The 

 recent summary of Chapman and Tilney (3) cites the conclusions 

 of the various authors and I would single out the reports of Picken 

 (7) and Robson (8) as those which are most significant. New 



