252 Prof. H. James-Clark on the Spongie ciliate 
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 tapering 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 flagella of the truly natant Flagellata; for whilst in 
the latter case the vibrations pass along the whole length of 
the czliwm, 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 Cyclidium, Duj. (non Ehr.), 
whose flagellum during reptation projects (from a deeply sub- 
terminal point of the convex side of the body) without lasioe 
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 ped 
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 us eee: to some remarks 
upon Actinophrys, in the ‘ Proceedings of the Boston Society of Natural 
Histery ’ for September 1863, p. 283, and republished in the ‘Annals and 
Magazine of Natural History’ for November 1864. 
