cally the conclusions deduced by me from a careful study of the astonishing characteristics of the apparatus. I have since corrected these conclusions by references to living objects, but I shall begin my observations by confining them at first to the uncorrected impressions made on the eye and mind by Lord Sydney G. Osborne's slides themselves, and introduce the corrected impressions subsequently, for, I think that a principle of observation of considerable importance will be well illustrated by so doing.

The information to be obtained from these specimens supplements in several interesting particulars the previous papers on the same subject noted below, and especially Mr. Gosse's well-known and important paper on the manducatory organs of the Rotifera. A reference to that highly original paper will show the extraordinary variations discovered by him in the organ in the different sections of the Rotifer family, and also the names which he has chosen for the different parts of the organ. The organs are symmetrical and bilateral, and consist of a pair of jaws. The teeth (unci) work horizontally, and are forced forward from behind by handles (manubria), to which their roots are attached; these manubria are armed sometimes with mallet heads (mallei), the same teeth (unci) are also attached at their points to blades (rami), and these rami draw the two sets of teeth by the points together, and themselves meet or cross each other at one extremity in a hinge (fulcrum), which gives them a scissor or tongs-like action, and in some cases the teeth work on an anvil (incus).

Of the figures which accompany this paper, Fig. 1, Plate X., is an anatomical diagram of the parts of the mastax of M. ringens. The teeth (unci), which I make out to be about fifteen in number, are seen below, at pp, having been removed from each jaw; their points of junction with their late supports are expressed in the case of each ramus by the serrated or turreted edges of that organ; these serrations in the diagram represent true sockets visible under a high power, particularly in the case of the large teeth after the removal of the teeth from the ramus. The basket-like organs d d are the manubria, the parts abc form the rami, f is the hinge, and the parts e will be explained subsequently. Fig. 2, Plate X., is a rough sketch of the general effect of the organ as seen looking towards the hinge, five of the teeth on each side having been removed to make the under parts visible.

Passing on to Fig. 4, Plate X., that figure affords a mechanical illustration to express in cardboard my views of the form of the ramus, and I will proceed to explain it. Take a thick piece of cardboard and cut from it a portion with an

เ

* See Williamson on M. ringens, Quar. Journal Mic. Sci.,' vol. i. p. 3, 1853; Gosse on M. ringens, idem, p. 71; 'Phil. Trans.,' 1856, vol. cxlvi. p. 419. In Rotifer vulgaris these serrations are very distinct.

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 underneath 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 flattened, 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 (f), 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, T. The Fig. 2, Plate X., shows the central blade of each ramus in