178 Transactions of the Boyal Microscopical Sociehj. 
outline as in the Figure 4, Plate X., notching the edge as in the 
figure, then fold the cardboard at the broken dotted line and turn 
the serrated edge upwards, and make the plane that carries that 
edge stand up perpendicularly from the plane to which it is 
attached. Double down the triangular projection E F G, and 
make it curl downwards and nnderneath the plane to which it is 
attached, then bend the handle, and you have, according to the 
view I take of it, a model of the ramus of the right-hand jaw, and 
a similar course will bring out the ramus of the left jaw. We thus 
have in the ramus a handle with two blades or leaflets and a 
triangular projection. Of these two blades I will, for the purpose 
of this essay, call the serrated blade the frontal blade, and the 
other the central blade, and keeping this mechanical picture in 
view, we will next consider its mode of action. 
The teeth [unci) are treated in Fig. 1, Plate X., as if they were 
fifteen separate teeth, but I feel satisfied that the fifteen are con- 
nected with each other by a membrane of some kind, and with this 
view Lord Sydney G. Osborne agrees. It is exceedingly delicate, but 
it throws up a soft pink hue whenever a strong concentrated flood 
of light, taken from the centre of the bull’s-eye condenser, is sent 
through it. It is well known to all observers of this rotifer, that 
the teeth of M, ringens, when in action, are bent like the closed 
knuckles, and we have, in fact, only to roll the knuckles, when 
closed, against each other, to obtain a practical illustration of the 
action of the jaws in the course of grinding food. In these slides, 
however, the teeth, as a rule, are very seldom bent, but lie flat 
or are slightly curved, and are seen on inspection to be flat- 
tened, watchspring-like weapons. Of these the two largest on 
each jaw show a central prominent line, see Fig. 5, Plate X. 
But though, as I have said, in the majority of the slides the 
teeth lie nearly flat, yet in a few of the slides, and particularly 
where the mastax is seen to be closed, they are found to be bent 
into the knuckle-like, rectangular appearance which they have in 
life, and the mechanical action by which this change is produced, 
from the flat to the rectangular view, is a most interesting subject, 
and one requiring careful attention, and I make it out to be as 
follows : — Suppose the handle of each ramus to move on the hinge 
(/), so that the frontal blades are made to approach each other 
face to face, and the teeth brought point to point ; now, if the 
free edge of the central blade keeps tilting upwards until it touches 
the under side of the teeth, then, as it travels onwards and 
upwards it will bend the teeth from beneath into an obtuse-angled 
attitude, and forcing forward, it will gradually reduce this angle 
to a right angle, and having done this, the teeth of each jaw will 
then meet in two right angles and form the letter T, — thus, IF. 
The Fig. 2, Plate X., shows the central blade of each ramus in 
