TRICHOCYSTS. 8 1 



crowded together and distributed in an even layer immediately beneath 



the cuticle throughout the whole extent of the cortex, their disposition with 



respect to the external periphery being everywhere perpendicular. Under 



certain conditions, including the application of artificial stimuli, such as 



weak acetic acid, these trichocysts become suddenly elongated, and their 



distal ends piercing the overlying cuticle stand out like fine, stiff, hair-like 



setae, beyond the cilia, around the entire circumference of the animalcule, 



frequently becoming entirely separated from their base of attachment. 



The names of Ehrenberg and Oscar Schmidt are most usually associated 



with the earliest discovery of these special structures, the first-named 



authority having recorded their presence in Bursaria (Panophrys) vernalis 



so long ago as the year 1832, and in which connection they are figured and 



described as minute prismatic rod-like bodies embedded beneath the cilia 



in the body-substance. By Oscar Schmidt, in the year 1849, similar rod-like 



bodies were reported to occur in Bursaria (Panophrys) leucas, and Para- 



mecium aurelia, their close correspondence with the rod-like bodies possessed 



by various Turbellaria being indicated. It has been recently elicited, 



however, by the present author that the existence of these trichocysts in 



Paramecium aurelia was discovered, and their characteristic aspect when 



extended figured and described, by our distinguished countryman John Ellis, 



more than a century ago, and at a time when microscopical science was 



quite in its infancy. With the imperfect magnifying apparatus employed 



by this investigator it was not possible to recognize the fine vibratile cilia 



by which the ordinary motions of the animalcule are accomplished, a 



circumstance which led him to attribute such a special function to the 



bodies in question ; this, however, in no way detracts from his merit as 



their first discoverer. Ellis's account of these trichocysts being of high 



intrinsic as well as classic interest, its reproduction in extenso is herewith 



appended. After recording his discovery of the locomotive organs, or cilia 



which he denominates " minute fins," in various species of Infusoria, which 



he sagaciously compares with the natatory organs or cilia then- recently 



described by Linnaeus as characteristic of the Ccelenterate genus Beroe, 



he proceeds to say : 



" I have lately found out, by mere accident, a method to make their fins (cilia) 

 appear very distinctly, especially in the larger kind of animalcula, which are common 

 to most vegetable infusions, such as the Terebrella (Paramecium) ; this has a longish 

 body, with a cavity or groove at one end, like a gimlet. By applying a small stalk 

 of the horseshoe geranium, G. zonale, Linn., fresh broken, to a drop of water in 

 which these animalcules are swimming, we shall find that they become torpid 

 instantly, contracting themselves into an oblong-oval shape, with their fins extended 

 like so many bristles all round their bodies ; the fins are in length about half the 

 diameter of the middle of their bodies. Before I discovered this experiment, I tried 

 to kill them by different kinds of salts and spirits, but though they were destroyed 

 by this means, their fins were so contracted that I could not discover them in the 

 least. After lying in this state of torpidity two or three minutes, if a drop of clean 

 water is applied to them, they will recover their shape and swim about immediately, 

 rendering their fins again invisible." 



