250 Martin, A Note on the Occurrence of Nematocysts and Similar Structures etc. 



at which it is developed to the point at which it is used. This 

 interesting subject was first opened up by the work of Hadzi, 

 and the behaviour of the Nematoblast in these cases seems to 

 present an interesting analogy to the behaviour of the Phagocyte 

 cells in Turbellaria, which carry the ingested Nematocysts from 

 the gut to their definitive position under the skin. To this point 

 I will return in the conclusion of this paper. 



In addition to the true Nematocysts referred to above, which 

 are I believe only developed in and characteristic of the group of 

 Coelenterates, certain structures have been described under the 

 name of Nematocyst in other animals. For the purposes of this 

 paper I have decided to divide all these structures into five 

 categories. 



(1) Autocnidae. 



By this term I wish to imply that the Nematocyst has been 

 developed singly, in a true Nematoblast within the tissue of its 

 possessor. The Autocnidae are I believe confined to and character- 

 istic of a single group of Metazoa the Coelenterates. 



(2) Cleptocnidae 1 ). 



Under this term I wish to include the Coelenterate Nematocysts 

 which have been ingested with the food and are found in an unex- 

 ploded condition in the tissue of their possessor (e. g. the Nemato- 

 cysts of Aeolids, Turbellaria, etc.). 



(3) Pseudocnidae. 



Under this term I wish to include a number of structures 

 which are almost certainly not homologous, and which have often 

 been confused with true Nematocysts. This group is a very hetero- 

 geneous one, it includes on the one hand structure containing a 

 spiral thread which can be discharged, e. g., the Nematocysts of 

 certain Nemertines. Structures which can under certain conditions 

 emit a thread, but in which the thread is not pre-formed within a 

 capsule (e. g v The so-called Nematocysts of Epistylis and Otoj>ln/ttt) 

 and a certain number of structures which have been described as 

 Nematocysts especially amongst the Turbellarm, and in which no 

 trace of a thread has been discovered. 



(4) Polar Capsules. 



These structures appear to be strictly analogous structures as 

 regards development, structure, and mechanism, to the Nematocysts 

 of Coelenterates, but they are confined to and characteristic of a 

 single group of the Sporoxoa. 



1) For the suggestion of this useful term I am indebted to my former Tut or, 

 Mr R. T. Giinther, of Magdalen College, Oxford. 



