470 Royal Society. 



and from all inferences as to the secular increase of the alluvial de- 

 posits, until he has had an opportunity of laying before the Society 

 an account of the far more extensive researches made in the district 

 of Memphis in 1S52, and during the last year in a series of pits 

 sunk in a line across the valley of the Nile, extending from the 

 Libyan to the Arabian Chain, in the parallel of Heliopolis. 



In the various excavations that have been made in the prosecu- 

 tion of this inquiry, many objects of art of historical interest have 

 been discovered ; but as these do not come within the province of 

 the Royal Society, the author proposes to give an account of them 

 in a memoir to be laid before another learned body. 



March 1, 1855. — Charles Wheatstone, Esq., V.P., in the Chair. 



The following communication was read : — 



" On the Structure, Functions, and Homology of the Manducatory 

 Organs in the Class Rotifera." By Philip Henry Gosse, A.L.S. 



In this paper the author institutes an examination of the mandu- 

 catory 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 Ehren- 

 berg 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 there- 

 fore 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 mandu- 

 cation : 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 ex- 

 tremity the buccal funnel, and on the dorsal side giving exit to the 

 asophagus. 



Within this sac are placed two geniculate organs (the mallei), 

 and a third on which they work (the ificus). Each 7nalleus consists 

 of two parts (the manubrium and the uncus), united by a hinge-joint. 

 The manubrium is a piece of irregular form, consisting of carina 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 com- 

 mon 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 

 each uncus rest upon the corresponding ramus, to which they are 



