CADET HAND 189 



the familiar desmonemcs or volvents, and the much less familiar 

 acrophores and anacwphorcs of the Siphonophora, which are col- 

 lectively called rhopalonemcs and have a sac-like tube rather than 

 the coiled or corkscrew tube of the desmonemcs. 



The stomocnidae show much more variety in form. They can be 

 divided into the haploncmcs, whose tube has no enlarged basal 

 portion or butt, and the hcteroncmcs which have a butt. Among the 

 haplonemes we find the familiar armed holotrichs and unarmed 

 atrichs, as well as partially armed forms we call basitrichs. These 

 haplonemes have a thread or tube of constant diameter and are 

 technically isorhizic. A second type of haploneme has an aniso- 

 diametric tube which may taper or be slightly swollen near the base. 

 These are the anisorhizic nematocysts of various siphonophores and 

 Tubularia. 



The heteronemes, which you recall have a butt, can be divided 

 into the rhahdoidcs whose butts are isodiametric and the rhopa- 

 loides whose butts are anisodiametric. The rhabdoides can in turn 

 be subdivided into masiifiophores with a terminal thread and 

 amastigophores which have no terminal thread, while the rhopa- 

 loides may be subdivided into eurijtclcs whose butts are dilated at 

 their distal ends and stenoteles whose butts are dilated at their bases. 



Further subdivisions of a number of the nematocyst categories 

 mentioned abo\e were proposed by Weill (10) but it is not neces- 

 sary to review them further here. Weill's system described a total of 

 eighteen different nematocyst categories, and in fact made it possi- 

 ble by applying the terms hoplotelic for armed threads and anaplo- 

 telic for unarmed threads to distinguish two sub-types within most 

 of the subdivisions of the heteronemes. 



Working from Weill's system still other kinds of nematocysts 

 have been described. Carlgren (2) divided mastigophores into 

 b-mastigophores and p-mastigophores, based on the appearance of 

 the end of the inverted butt. The p-mastigophore was the type Weill 

 (10) had described and the b-mastigophore was a new category 

 which in its unexploded condition looked like a basitrich but when 

 exploded looked like a mastigophore. 



Another worker, Cutress (5), using the light microscope de- 

 scribed two further categories of nematocysts, q-mastigophores and 

 macrobasic p-mastigophorcs, and proposed the elimination of 



