252 Prof. IL James-Clark on the Spongia3 ciliatje 



that it appears, without close observation, to be a mere taper- 

 ing prolongation of this region. Yet it is neither related to 

 the body in the latter sense, nor an extension of it from any 

 point of view, but is as strictly an appendage as any form of 

 vibratile cilia*, and alike as incapable of contraction. It is so 

 stout and thick that one need not be surprised to find Ehren- 

 berg, in the absence of a knowledge of the structure of this 

 animalcule, mistaking the scarcely tajoering flagellum for the 

 frontal prolongation of a Trachelius. Usually it is about half 

 as long again as the body ; but that of very large animals 

 often greatly exceeds this proportion. Its mode of action, as 

 a propulsive organ, is not like that most frequently exhibited 

 by the jiagella of the truly natant Flagellata ; for whilst in 

 the latter case the vibrations pass along the whole length of 

 the cilium, in the former they are confined to its distal end ; 

 and, moreover, they seem to be different in character, since, 

 instead of simply undulating in a more or less restricted plane, 

 the flagellum twirls at the tip rather after the manner of a 

 revolving helix. 



This method of progression is singularly modified by a 

 rhombic meniscoid species of Gyclidium^ Duj. (non Ehr.), 

 whose flagellum during reptation projects (from a deeply sub- 

 terminal point of the convex side of the body) without flexure 

 almost to its tip, and then simply bends with frequent and 

 vigorous strokes in the form of a hook, which it applies side- 

 wise against the surface over which the creature is passing, 

 and drags it after it, tilted over on one of its flanks, in a hitching 

 sidelong manner. 



As a tactile organ, and for the purposes of prehension, the 

 flagellum appears, by its great flexibility and vigorous action, 

 to be eminently capable. Feeling about it with all the appa- 

 rent expectation of finally meeting with something, the ani- 

 malcule keeps its proboscis in a constant quiver, lashing it 

 backward and forward in the meanwhile, or thrusting it along 

 its flanks and then abruptly withdrawing it, very much after 

 the manner of a Lacrymaria. When a particle of food is 

 brought near the mouth (m), it is, as it were, coaxed into it by 

 the light pulsations of the flagellum^ apparently assisted by 

 the movements of the buccal margin. 



The eye-spot {s) , so called, naturally comes under considera- 



* As my views in regard to the relation of vibratile cilia to underlying 

 cells may not be fully understood in this allusion, I would refer to my 

 published opinion on this subject, in a note appended to some remarks 

 upon Adinophrys, in the ' Proceedings of the Boston Society of Natural 

 History' for September 1863, p. 283, and republished in the 'Annals "and 

 Magazine of Natural History ' for November 1864. 



