OF THE PROTOZOA. CILIATA. 287 



a certain point, or when the reproductive process consequent upon it differs 

 from that seen in Chilodon, appears to involve the final disappearance both 

 of generally diffused cilia and of specially organized ciliary wreaths. 



The an-est of the motion, and the ultimate disappearance of cilia, are phe- 

 nomena attendant also on the death, or on the approaching diffluence, of ani- 

 malcules — when the surrounding w^ater dries up, or when their vitality is 

 injiu'ed by chemical agents or by physical forces, such as electricity and heat. 

 Stein, however, states that, although the animalcule, e. g. a Paramecium, is 

 killed by the addition of very dilute acetic acid, yet its cilia continue visible 

 and of their normal length. Cohn behoved the cilia to be very much longer 

 than Ehrenberg represented ; but, as Stein affirms, this notion originated from 

 an unnatural appearance consequent on the dying state of the animalcule, from 

 evaporation of the surrounding water ; and he adds that a similar elongation 

 of cilia appears immediately at the point where strong acetic acid comes into 

 contact with the suiface. But this explanation has since been set aside by 

 Prof. Allman's discovery of the existence of trichocysts, or thread-cells, 

 within the subtegumentary layer of the body (XXXI. 1-4), to which he at- 

 tributes the phenomena observed and discussed by Cohn and Stein. 



An instance of a temporary formation of cilia is seen in the VorticeUina 

 and OpTirydina when the offspiing, formed by fission or by gemmation, is pre- 

 pared to detach itself from the parent being. Under such circumstances, and 

 prior to the development of the interior retractile ciliary organ, a wreath of 

 ciha makes its appearance (XXVII. 4, 11) near the posterior extremity — but 

 which, indeed, for the time, advances first in swimming, and continues to do 

 so until the animalcule has attached itself and proceeds to unfold the ciliated 

 apparatus at its head. 



In the above account, reference has been chiefly made to vibratile cilia, but, 

 as before noticed, there are tegumentary processes of larger size, coarser and 

 stiffer, and withal not vibratile, although moveable. Such serve frequently 

 as special organs of locomotion, or of prehension, or of both, and may also be 

 occasionally considered weapons of offence and defence. Accordiag to their 

 form they are named set<x, or bristles ; uncini, or hooks ; cirrif styles and 

 filaments. 



Some of these terms are both loosely defined and used. Thus the bristles 

 so called of one author, are spoken of by another as cirri, or styles or fila- 

 ments, — the structures thus variously called being long bristles, mostly taper- 

 ing, and either straight or but slightly ciuwed. The term " czn-i " (in EngEsh, 

 tendrils) should be disused, both as being unnecessary and also as conveying an 

 erroneous conception ; for no organs like tendrils exist among Protozoa. Un- 

 cini (hooks) are very thick at the base, strong, curved, and comparatively short 

 processes (XXIX. 15, 17) ; styles are stout setiform bristles, articulated at 

 their base to the cuticle, and of considerable length (XXYIII. 10 ; XXV. 

 350, 351). These last-named processes, Lachmann tells us, are sometimes 

 spHt up at the apex into two, or even as many eight, parts, as happens in 

 various Euplotes (for instance, E. Patella, in which species, moreover, one 

 style bears a number of small lateral setiform branches). The divided styles 

 occur at the posterior extremity, and are trailed along in the movements of 

 the animals, and only occasionally employed in pushing them forwards, whilst 

 the uncini in advance serve for actual creeping and cHmbing. As examples 

 of these tegumentary appendages, may be adduced the setae of Urostyla and 

 Kerona ; jthe uncini, setae, and styles of OccytHchina (XXVIII. 10), Euplotes 

 (XXV. 350-353), and ofPloesconia. Intermediate grades, between the highly- 

 developed setose processes cited and ordinary vibratile ciha, may be seen in 

 the larger and more rigid ciliary structures alluded to above as often found 



