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 ease 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

* 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.