Page:Proceedings of the Royal Society of London Vol 7.djvu/310

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In this paper the author institutes an examination of the manducatory organs in the class Rotifera, in order to show that the various forms which they assume can all be reduced to a common type. He further proposes to inquire what are the real homologues* of these organs in the other classes of animals, and what light we can gather, from their structure, on the question of the zoological rank of the Rotifera.

After an investigation of the bibliography of the class from Ehrenberg to the present time, in which the vagueness and inexactitude of our knowledge of these organs is shown, the author takes up, one by one, the various phases which they assume throughout the whole class; commencing with Brachionus, in which they appear in the highest state of development. Their form in this genus is therefore taken as the standard of comparison.

The hemispherical bulb, which is so conspicuous in B. amphiceros, lying across the breast, and containing organs which work vigorously against each other, has long been recognized as an organ of manducation: it has been called the gizzard; but the author proposes to distinguish it by the term mastax. It is a trilobate muscular sac, with walls varying much in thickness, receiving at the anterior extremity the buccal funnel, and on the dorsal side giving exit to the æsophagus.

Within this sac are placed two geniculate organs (the mallei), and a third on which they work (the incus). Each malleus consists of two parts (the manubrium and the uncus), united by a hinge-joint. The manubrium is a piece of irregular form, consisting of carinæ of solid matter, enclosing three areas, which are filled with a more membranous substance. The uncus consists of several slender pieces, more or less parallel, arranged like the teeth of a comb, or like the fingers of a hand.

The incus consists of two rami, which are articulated by a common base to the extremity of a thin rod (the fulcrum), in such away that they can open and close by proper muscles. The fingers of