OF THE MANDUCATORY ORGANS IN THE CLASS ROTIFERA. 
425 
form and motions. By old observers the vigorous workings of its internal parts 
caused it to be mistaken for a heart; but it has long been recognized as an organ 
of mastication. Dr. Ehrenberg sometimes calls it Kauorgan, but more generally 
Schlundhopf, and its contents Kau-apparat. M. Dujardin speaks of it as le hulbe 
pharyngien. Von Siebold calls it a pharynx ; and English zoologists have generally 
used the term gizzard. 1 hope to prove that it is neither a gizzard nor a pharynx, 
but a true mouth: in the mean time, however, whatever its homological value, it is 
doubtless a form of apparatus which has no parallel in other classes of animals, and 
therefore deserves a proper appellation. I propose then to appropriate to the sub- 
globose muscular bulb, which contains the manducatory organs in most Rotifera, 
the term mastax. 
21. The mastax, with its contents, is found in the highest degree of development 
in the genera Brachionus, Euchlanis, and some of the Hydatinrea. It is usually more 
or less globose in form, composed of three lobes, which are confluent anteriorly, with 
a common rounded outline; but separated posteriorly, one lobe diverging towards 
the ventral side, the others laterally, and a little dorsally ; so that a posterior aspect 
would assume the outline of a trefoil. The general form is sub-hemispheric in Bra- 
chionus and its allies ; that of an oblate spheroid in Euchlanis ; a prolate spheroid in 
Notommata aurita ; cordate in Notommata petromyzon ; sub-triquetrous in Plagio- 
gnatha ; triglobular in Notommata clavulata ; purse-like in Mastigocerca ; irregularly 
oblique in Synchasta and Polyarthra ; and wanting in Floscularia. 
22. In substanee it varies from a state in which its walls are thick and solid, com- 
posed of dense muscular fibre, with little cavity, as in Brachionus, to one in which it 
forms a capacious sac, with thin, apparently membranous, parietes, as in Furcularia. 
23. The anterior side of the mastax is perforate, its walls here merging into the 
tube of the huccal funnel. It is perforate also on its dorsal aspect ; whence the 
oesophagus issues to join the stomach. 
24. Let us now examine in detail the mastax, \n the modifications which it assumes 
in various species. In Brachionus urceolaris (Plate XVI. figs. 1 to 10), it is a dense, 
colourless, highly- refractive mass of muscles, sub-hemispherical, distinctly trilobate 
posteriorly, and cleft deeply on the ventral side of its anterior surface (fig. 1). Within 
it are placed two geniculate organs {h), which, from their resemblance in form and 
action to hammers working on an anvil, I have elsewhere named mallei ; and a third 
{f), still moie complex, which I call the incus. These three pieces are not arranged in 
the same plane ; for the mallei approach each other a little dorsally, while the incus 
is placed on the ventral side of the centre, its stem pointing considerably towards the 
same side. Thus each of the three organs corresponds to, and occupies the centre 
of, one of the lobes of the mastax. This obliquity of tbe parts with respect to each 
other, and to the planes of the body, is one cause of the great difficulty which attends 
an endeavour to reconcile the various aspects of this organ in any intelligible manner. 
25. Each malleus consists of two principal portions, articidated with each other by 
