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



Eine Nesselkapsel aus dem Riissel von C. urticans 1st 0.1 mm 

 lang, aber nur 0.002 mm breit. Ihr Faden erscheint auch bei 

 rnittleren Vergrofierungen noch haarfein " 



Unfortunately I have only had one opportunity of examining 

 these Nematocysts in Micrura purpnrea and Cerebratulus urticans, 

 and my attempts at obtaining further examples of these animals 

 have failed. In both these cases I can feel little doubt from the 

 examination both of fresh material and of sections that we are 

 dealing here with capsules containing a pre-formed thread which 

 is everted in a precisely similar manner to that of a Coelenterate 

 Nematocyst. In the case of the Nematocysts of Micrura it was 

 however interesting to observe that the thread swelled up and 

 disappeared within 10 minutes of the explosion. It is perfectly 

 clear that these cases of the occurrence of Nematocysts in Nemer- 

 tines cannot be regarded as Cleptocnids, and these structures seem 

 to differ essentially from the true Nematocysts of Coelenterates 

 only in two points (1) in their development in packets in a single 

 cell, (2) in the case of Micrura in the disappearance of the thread 

 shortly after explosion. 



II. (5) Molliisca. 



In the group of Mollusca there are two instances of occurrence 

 of Nematocysts. 



The first is the well-known case of the Nematocysts of Aeolids 

 which has been so brilliantly worked out by Grosvenor. 



The second is the rather obscure case of their occurrence in 

 a Cephalopod, Tremoctopus microstoma. 



Cleptocnids in Aeolids. 



It is to the work of Grosvenor that we owe the present 

 acceptance of the view that the Nematocysts in Aeolids are derived 

 from their Coelenterate prey. In his paper on the Nematocysts 

 of Aeolids (Proc. Roy. Vol. 72) Grosvenor gives a short his- 

 torical account of the origin of this view. From this it appears 

 that the Nematocysts of Aeolids were found by Alder & Hancock 

 who however in their first paper formed no very clear view as to 

 the nature of these structures. Grosvenor the states n. that 



"By the time of writing the 'Monograph of British Nudibran- 

 chiata', Alder and Hancock had arrived at a true conception of 

 the nature these bodies. 



In December, 1858, T. Strethill Wright read a paper before 

 the Royal Physical Society of Edinburgh, in which he maintained 

 that the cnidae, or thread cells of the Aeolidae, were derived from the 

 Hydroids on which they fed. He mentions that the same idea had 

 previously occurred to Huxley and Gosse, and that the latter 

 had suggested the method of proving its correctness." 



