180 Transactions of the Eoyal Microscopical Society. 
Thus far we have dealt entirely with Lord S. G. Osborne’s 
slides ; but the subject receives remarkable and striking illustration 
on the point at which we have now arrived, if we pass on to the 
mastax of the living Conochilus. In the slides of M. ringens, 
the hinge is hopelessly confused by flattening, and I confess 
I could make nothing of it ; but good fortune brought me a rich 
supply of Conochilus in February, and as the same organ in that 
rotifer is almost identical with that of Melicerta, a description 
of the action of its parts will be found of great value in enabling us 
to grasp the whole subject. 
Even with Mr. Gosse’s paper on the mastax of rotifers to help 
us, the living Conochilus in action, transparent as it is, forms a 
hard puzzle to the eye of the observer. But a familiarity with 
Lord Sydney G. Osborne’s slides at once makes its investigation 
comparatively easy. There is but one position which Conochilus 
can take that will give a comprehensive view of the more im- 
portant details of the organ, and unfortunately the animal rarely 
assumes it, and it requires patience to wait for it, but after close 
attention I have made out the characteristics of the organ to be as 
follows. The aspect of the teeth (iinci), attached by their points 
to the rami, and by their roots to baskets (inanubria), is exactly 
like that of M. ringens ; one picture, in fact, does for both. 
The teeth are quite straight, they lie very near together, like 
ridges of plaited paper ; there are five larger teeth on each side as 
against three in M. ringens. The number of teeth, fifteen to 
eighteen, is about the same for each rotifer, and they are connected 
by a delicate membrane. The alulm are there in striking distinct- 
ness, and whenever the mastax is viewed sideways, they are seen 
hanging down underneath very clearly and in broad, strong outlines. 
Plate XL, Fig. 6, gives a mechankial drawing of the rami, and the 
alulw, and the hinge, but the teeth and the baskets have all been 
removed. The plan of construction of each ramus will be seen to 
be much the same as that of M. ringens. There is what I have 
called frontal blade, which carries the points of the teeth, but at 
one end it is so depressed and insignificant that it really hardly 
deserves the name of a distinct blade, and I doubt if it is more at 
the lower end of it than a thickening of the straight edge of the 
central blade of the ramus. At the point, however, where it rises up 
and leaves the edge of the ramus, and just where the large teeth are 
carried, it appears of a distinctive character. I have made a few 
turreted spaces in the edge to show where the points of the teeth are 
carried, and I may add that I have seen the edge actually serrated at 
that place and in more than one specimen. From the free edge of 
the central blade, just as in M. ringens, the alulm are seen hanging 
down and curling under the ramus and towards each other. With 
respect to the left-hand ramus, I have represented its alula by 
