210 Prof. H. James-Clark on the Spongie ciliates 
with which the free end of each one is endowed. The whole 
bristling mass revolves alternately from right to left and from 
left to nght, whirling upon its slender pivot with such a degree 
of freedom that one might almost suspect that it merely rested 
upon it, and had no truer adhesion to it than the juggler’s top 
to the end of the bdton upon which it spins. The largest 
of these twirling groups contains as many as fifty fusiform 
bodies; but most frequently not more than half that number 
are grouped together; and from this they vary in decreasing 
numbers dgwn to only one or two (fig. 48) upon each filamen- 
tous twig.” In the last instances the bodies are comparatively 
quiet, scarcely moving out of focus at each spasmodic twitch 
of the arcuate filament. On this account, and because they 
offer an unobstructed view, the latter are by far the most 
available as objects for the investigation of their internal 
organization. | 
“The relationship of the individual monads to the whole 
colony must, however, be studied where they are more nume- 
rously congregated, since, as will be shown presently, each 
monad sustains a definite relation to every other one and to the 
twig to which it is attached.” 7 
“Form &c.—The adult monads (figs. 47, 48, md) have a 
truncate fusiform shape, and are slightly but quite appreciably 
flattened on two opposite sides, so that, in an end view, they 
appear to be broadly oval transversely. The attached end 
tapers gradually to a point; and on this account it is difficult 
to determine where the body ends and the twig begins. All of 
the members of a group radiate from a common point of at- 
tachment, to which they adhere by their tapering filamentous 
ends (fig. 48, pd!). ‘The free end is truncate; but one corner 
of it (as if in continuation of the line along which the opposite 
flattened sides meet) projects in the form of a rather blunt tri- 
angular beak (/p). At the inner edge of the base of this beak 
lies the mouth (m), to which the former, as frequent observa- 
tion has proved, acts as a 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 (md) is at- 
tached to its mooring in such a position that its flattened sides 
lie parallelwise with those of its nearest neighbour; and the 
beak (/p) projects from that corner of the head which is most 
distant from the twig (pd). To give a full idea of the pecu- 
liarity of this arrangement, it must be stated here that the 
rigid, arcuate, spasmodically twitching filament (2) mentioned 
