1895.] NATURAL, SCIENCES OF PHILADELPHIA. 167 



THE TRUE NATURE OF THE SO-CALLED "NETTLE-THREADS" OF 



PARAMECIUM. 



BY JOHN A. RYDER. 



It is well known that if Paramcecium aurelia is hurt or irritated 

 in any way that it will discharge from its cuticle what appear to be 

 filaments. This has been known for more than a century, for Elliot 

 in the Philos. Transactions of the Royal Society for 1769, pi. VI, 

 p. 150, gives a very good figure of a P. aurelia with these threads 

 projecting from its surface produced by the juice of the horse-shoe 

 geranium. Dr. G. J. Allmau in Vol. Ill of the Quar. Journ. of 

 Microscop. Science (1855), nearly a century later, upon reinvestiga- 

 ting this subject, comes to the conclusion that these discharged 

 threads are of the nature of nettling or defensive organs and that 

 they are discharged from minute oval or elongate cysts that are 

 closely imbedded in the ectosarc just beneath the cuticle of these 

 organisms. Allman also concludes that they are not identical with 

 the cilia which thickly clothe the organism. Various reagents are 

 known to cause this discharge of thread-like processes from the cuticle 

 or surface of Paramcecium, but no reagent that I know of does this 

 so effectually as tannic acid, the peculiar poteucy of which, for this 

 purpose, was first pointed out by H. Warrington (Journ. Roy. 

 Microscop. Soc, 1884). 



Most naturalists who have written in recent years upon the 

 structure of the Protozoa have accepted Allman' s statement that the 

 threads discharged by Paramcecium are not ciliary in nature. 

 Lankester, among others, makes such a statement very positively. 

 Fortunately there are two ways in which to test the truth of this 

 statement. 



1. It so happens that if a pretty strong solution of tannic acid is 

 used these threads are entirely detached from the body of Para- 

 moeciiim, if the reagent is allowed to act long enough. Endosmotic 

 action is also thus set up so that the cuticle is lifted off of the under- 

 lying ectosarc, which, together with the endosarc, now shrivels into a 

 disorganized, granular mass. The cuticle is seen to be thin and to 



