188 THE BIOLOGY OF HYDRA : 1961 



as genera, families or even orders, and in the broad view even 

 classes. Second, as a student of coelenterates I am interested in the 

 biology of these animals, and the nematocysts are intimately in- 

 volved in numerous aspects of the lives of coelenterates. 



There have been several attempts to classify nematocysts and 

 some of the results of these have come down to us in the form 

 of such useful and descriptive names as penetrants and glutinants. 

 However, it was not until the elaborate system of Weill (10) was 

 published that any real uniformity of nomenclature of nematocysts 

 was arrived at. With the introduction of Weill's terminology some 

 people complained that the system was too clumsy and the names 

 too long to be useful. For example the commonest penetrant of 

 many anthozoans could be called a hoplotelic microbasic masti- 

 gophoric rhabdoidic heteronemic stomocnidic nematocyst, or a 

 stenotele could be called a stenotelic rhopaloidic heteronemic 

 stomocnidic nematocyst. In common practice, and as Weill's termi- 

 nology is being applied, the names microbasic mastigophore (or 

 just mastigophore) and stenotele suffice. Weill's system is only for- 

 bidding when one first meets it, but it is a defined system which 

 makes possible far greater accuracy in communication than any 

 other so far devised. To use the full nomenclature, as in the exam- 

 ples I cited, is just as absurd as to start the name of some species 

 with the phylum name, add in the names of the class, order and 

 family and finally tack on the specific binomial. 



Weill's system recognizes two categories of cnidae, spirocysts 

 and proper nematocysts. Spirocysts are restricted to the zoantharian 

 anthozoans while all coelenterates have nematocysts. The struc- 

 ture and function of spirocysts are obscure. Weill (10) believes that 

 spirocysts have but a single layered wall and it is extremely rare 

 to see a spirocyst which has everted its thread. Cutress (5) has ar- 

 gued rather convincingly that spirocysts are nematocysts and from 

 his comments one could conclude that they represent a form of 

 holotrichous nematocyst. The test of this conclusion will undoubt- 

 edly come when a study of these cnidae is carried out with an 

 electron microscope. 



The nematocysts proper have two major subdivisions, astomo- 

 cnidae whose tubes are closed and stomocnidae with tubes open at 

 the tip. The astomocnidae are divided in turn into two categories. 



