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



A Note on the Occurrence of Nematocysts and Similar 



Structures in the Various Groups of the Animal Kingdom. 



By C. H. Martin, M. A., The Hill, Abergavenny. 



With 8 Text figures. 



I. Introduction. 

 II. Nematocysts and Similar Structures in 



1. Protozoa. 



2. Sponges. 



3. Turbellaria. 

 1. Nemertinea. 



5. Mollusca. 



6. Chordata. 



III. Conclusions. 



IV. Literature List. 



V. Description of Figures. 



I. Introduction. 



The number of groups of the animal kingdom in members of 

 which Nematocysts have been described has not, I believe, been 

 commonly recognised, since the references in the literature are very 

 scattered, and in most instances have not found their way into 

 the text books. 



In this paper I have tried to put together all the references 

 I could find to the occurrence of Nematocysts in various animals, 

 and although this list is probably by no means exhaustive, still it 

 includes representatives of no less than six Phyla (viz., Protozoa, 

 Sponges, Turbellaria, Nemertinea, Mollusca, Chordata). In many of 

 these instances the animals are so rare that it seems hopeless to 

 delay publication until a personal examination has been made of 

 each case, so that I have thought under the circumstances that the 

 publication of a summary examination of the evidence even in these 

 cases might not be without value. 



The terminology of Nematocysts is in such a confused state 

 that it will first be necessary to define clearly in what sense the 

 various terms are used in this paper, since in most cases it seems 

 quite impossible to harmonise the various usages to which these 

 terms have been put by previous authors. 



A Nematocyst in a Coelenterate consists of a capsule containing 

 a rolled-up thread and an amorphus substance; the thread can be 

 everted when the Nematocyst is placed under suitable conditions, 

 and then remains attached to the capsule (distinction from the 

 Spirocysts of Anthozoa). 



A Nematocyst or Cnida is apparently always developed singly 

 in a special cell, the Nematoblast or Cnidoblast. The word Nemato- 

 blast (= Cnidoblast) is here used for the cell which is about to 

 form or has formed a Nematocyst. This seems to be the most 



