KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 59 



Nematocysts. — The nematocysts, like the ocelli of the dinoflagellates, are 

 among the most highly specialized organelles found in the Protozoa. Like 

 them also the nematocysts of Polykrikos and Nctmif,odiniu)H,, similar in struc- 

 ture to the nematocysts of the Coelenterata, represent a type of specialization 

 that is metazoan in its character and occurence rather than protozoan. 



The fact that these organelles are of rare occurrence in the Dinoflagellata 

 and are totally unknown in the remainder of the Mastigophora naturally raises 

 the query whether they may not be adventitious bodies, ingested either with 

 fragments of coelenterates as food, or after discharge into the water from some 

 coelenterate of the plankton. This suspicion of extraneous origin is heightened 

 by the fact that such cases are kno\\Ti in the Metazoa, as in the mollusc Aeolis, 

 in which the nematocysts are introduced into the body with its food (Grosvenor, 

 1903). 



Several facts point towards the conclusion that the nematocysts of both 

 Polt/krikos and Nematodinimn are not adventitious bodies, but are normal 

 structures in the organisms in which they are found. First and foremost of 

 these is the fact that they occur in at least four different species, have been 

 found in every individual of these species thus far examined, and have not been 

 found in other forms feeding on the same plankton and often showing the same 

 kind of ingested organisms. 



Fragments of coelenterates have not been observed as food particles nor 

 have free nematocysts been found in the plankton in which Polifkrikos and 

 Nematodimum occur. Contact with the sea water is usually sufficient to bring 

 about a discharge of the coiled filament of the nematocyst. The young stages 

 of the nematocysts deliquesce very rapidly in sea water on disintegration of 

 the body of Polykrikos. If they are adventitious it would be necessary for 

 them to resist the disintegration of the sea water prior to ingestion, provided 

 they were found free in the water. If ingested in coelenterate tissue the 

 matured nematocysts must endure ingestion without discharge. The structure 

 of the nematocysts is always constant, which might not be the case if they were 

 adventitious unless they were always derived from the same species of coelen- 

 terates. This would postulate a habit of selective feeding of which we have 

 not the slightest evidence. On the contrary, Polykrikos is omnivorous in its 

 feeding habits. 



Faure-Fremiet (1914) was the first investigator who attempted to solve the 

 mysteries of the development of these peculiar organelles, as also did Chatton 

 in a series of papers in 1911. The latter figured a cycle of development (fig. G) 

 which leaves many points still open to question. Both of these investigators 

 maintain as the result of their investigations the conclusion that these are 

 normal structures in Polykrikos, and not parasitic or adventitious in their 

 origin. 



Faure-Fremiet also pointed out the similarities between the nematocysts of 

 this genus and those foimd in Campanella umhellaria {Epistylis iimhellaria) . 



