Journal 



OF THE 



NEW-YORK MICROSCOPICAL SOCIETY. 



Vol. IV. JULY, 1888. No. 3. 



NOTES ON THE THREAD-CELLS OF CERTAIN CCE- 

 LENTERATE ANIMALS. 



BY CHARLES F. COX. 

 {Read March 2d, l888.) 



Thread-cells, lasso-cells, filiferous capsules, urticating organs, 

 cnidae, or nematocysts, as they are variously called, are usually 

 set down as characteristic of the whole sub-kingdom Coelenter- 

 ata, although their existence has not been actually demonstrated 

 in every order of either the Hydrozoa or the Actinozoa. Nor is 

 it certain that they are confined to coelenterate animals. Prof. 

 AUman claims to have observed the emission of urticating fila- 

 ments by a species of Bursaria, and there is reason to believe 

 that they occur in other infusoria, and perhaps in some anne- 

 lids. They have been reported to exist likewise in certain 

 naked moUusks, though it is still a disputed question whether 

 in such cases they are not derived from coelenterate animals 

 upon which the moUusks feed. In general, however, they may 

 be said to be the peculiar property of tentacled animals, and 

 there is good evidence upon which to regard them as organs of 

 offence and defence. 



When matured and fitted for their special function, these or- 

 gans are situated in the outer layer, or ectoderm, and are 



Explanation of Plate \%. 



Figs. III., IV. and V., are process reproductious of photographs from nature ; 

 Fig. III. showing the cell with the thr ad partially emitted, Fig. IV. the fully 

 extended thread, and Fig. V. two empty cells with the clear spaces at the 

 bases of the attached threads. 



Figs. I. and II., are modifications of Fig. III., made as diagrammatic representa- 

 tions of the cell before and at the beginning of the extrusion of the thread. 



