432 Prof. H. James-Clark on the Structure and 
this beak lies the mouth, to which the former (as frequent ob- 
servation has proved) acts asa lip or prehensile organ when food 
is taken into the body. The prevailing tint is a more or less 
uniform light gamboge, without the least trace of an eye-spot 
of any colour. 
A most singular uniformity prevails in the arrangement of 
the several members of a group. Each monad is attached to its 
mooring in such a position that its flattened sides lie parallelwise 
with those of its nearest neighbour; and the beak projects from 
that corner of the head which is most distant from the twig. 
To give a full idea of the peculiarity of this arrangement, it 
must be stated here that the rigid, arcuate, spasmodically twitch- 
ing filament mentioned above is attached close to the mouth, 
and invariably curves away from the beak, and consequently 
always toward the pedicel of the colony. One is forcibly re- 
minded by this of the systematic relation of some of the flowers 
of Labiate, with their stamens projecting far beyond the upper 
lip of the corolla. The globose heads of the Menthe are particu- 
larly good examples for illustrating this similitude. 
Prehensile organs.—The only motile organs which this animal- 
cule possesses are preeminently prchensile in character; and 
their apparent appropriation to the office of propulsion, when a 
colony breaks loose from its attachment, I can scarcely doubt is 
an accidental one, inasmuch as the arcuate cilium continues its 
spasmodic twitching without any apparent deviation from its 
usual mode of action. 
There are two cilia, of very unequal size, attached to the trun- 
cate end of the body. The larger one of these has already 
been mentioned casually, as a rigid, arcuate filament. It does 
not taper, but has a uniform thickness from base to tip, and is 
about half as long again as the body. It arises near the base 
of the triangular beak, but appears to be separated from the 
latter by the mtervening mouth. When quiet it appears like a 
bristle, and projects in a line with the longer axis of the body— 
at the base bending slightly toward the beak, and then sweeping 
off in a moderate but distinct curve in the opposite direction, so 
that on the whole it presents a long drawn-out sigmoid flexure. 
The plane of this curve lies in strict parallelism with the plane 
of the greater diameter of the body ; in fact it may be said to be 
a direct continuation of it. It does not appear to have the cha- 
racter of a flagellum, except when assisting the smaller cilium to 
convey the food to the mouth; and then it lays aside its rigid 
deportment and assumes all the flexibility and wavy vibration 
of the prehensile organ of an Astasia. 
The smalier cilium 1s an excessively faint body, and almost 
defies the detective powers of the highest objectives, This is 
