An Aid in the Study of Nematocysts. 235 



XXV.— An Aid in the Study of Nematocysts. By T. H. Taylor, M.A., 



Zoology Department, University of Leeds. 



(Received 23rd October 1911. Read 27th November 1911.) 



Although nematocysts have long been a favourite study with zoologists, 

 there are still many obscure points concerning their structure, function and 

 development, and it is perhaps beyond the reach of any one investigator 

 to give from all points of view a clear and convincing account of these 

 interesting objects. The present note on the subject aims merely at devising 

 an experimental method of studying the process of eversion. 



With regard to the structure of the filament itself, there is some differ- 

 ence of opinion as to whether the free end is open or closed. The uncertainty 

 on this point is perhaps due to the fact that nematocysts, at time of dis- 

 charge, frequently fail to complete the process of eversion, in which case the 

 real end of the filament does not become exposed to view. Moreover, even 

 when eversion is completed and the terminal part of the filament fully 

 extended, the fineness of detail exhibited by this region renders it difficult 

 for the eye to determine whether or not there is an aperture at the end. 

 Failing more direct evidence we may, however, infer from the following 

 considerations that a filament, when completely everted, opens freely to 

 the exterior : — (1) When, as sometimes happens in a favourable preparation, 

 the filament completes its eversion in air under a cover-glass, the fluid 

 contents, when passing out, collect into a pool on the glass surface. (2) The 

 forcible ejection of the fluid, setting up eddies in the preparation, 

 scatters any particles which happen to be near the end of the filament. 

 (3) The secretion contained in the capsule, when stained, can be seen to 

 pass through the filament and flow out at the end. (4) Further indication 

 is afforded by the fact that the secretion has the property of precipitating 

 certain dyes. Thus, for example, in Hydra, when the capsules are exploded 

 in a dahlia solution, a little cloud of precipitate immediately appears at the 

 end of each filament. Although it is clear from these facts that a filament 

 when fully everted terminates in an aperture, there is, it should be added, 

 no evidence to show that this is also the case before eversion, when the 

 filament is still coiled up within the capsule. 



The large nematocysts of certain Actinians are, in the fresh condition, 

 very favourable for study, and when, as often happens, they become 

 isolated in the field, a good opportunity is afforded of watching how 

 the capsule and filament each behave during discharge. The observer, 



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