292 Characteristics of Rotifers. 



paratus most highly developed, and we may select a Brachion 

 as our leading example. The preceding figure (1) of the mastax 

 of Brachionus urceolaris, is copied from Mr. Gosse, and it 

 will be more easily understood if we placed near it another 

 sketch, Fig. 4, copied from the same writer, of the gizzard 

 of the Notommata clavulata. 



In the Brachion mastax we see two, to use Mr. Gosse's 

 words, " geniculate organs," b, which he likens to hammers 

 working on an anvil, and names mallei, and a third, /, still 

 more complex, the incus (an anvil). 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 to- 

 wards the same side. . . . Each malleus consists of two princi- 

 pal portions articulated with each other by a powerful joint, 

 which seems to be ginglymate in. its character, admitting of 

 motion in one plane only, . . . the inferior portion of the mal- 

 leus, which I call the manubrium (handle), c, is an irregularly 

 curved piece, shaped somewhat like the scapula of a mammal, 

 knotted on its broad and flattened at its lower or fine end, where 

 also it is twisted on one side, ridges run down it on both the 

 exterior and interior surfaces, the head is obliquely truncate, 

 and it is this oblique surface, d, that is joined to the superior 

 portion, e, which, from its prevalent form in the other genera, 

 rather than in this, I call the uncus (hook) .... It consists of 

 five or six finger-like processes (Figs. 2 and 3), set parallel to each 

 other, and separated by narrow interspaces, which appear to 

 be occupied by a thin membrane. . . . The incus, /, consists 

 of distinct articulated portions. The principal are two stout 

 rami, g, resting on what appears to be a slender pedicel (ful- 

 crum b), but viewed laterally, the fulcrum is seen to be a thin 

 plate to the edge of which the rami are jointed, so that they 

 open and shut like a pair of shears. Each ramus is a thick 

 somewhat trigonal piece with the outer side rounded, the 

 upper side hollowed, and the inner side flat, and in contact 

 with the corresponding face of its fellow, in a state of repose. 

 The uncus of each malleus falls respectively into the concavity 

 of each ramus, and is fastened to it by a stout triangular muscle." 

 The two unci alternately recede and approach, and at the same 

 time the motion is complicated by a twist of the manubria. 

 " The incus also has considerable motion, sometimes the 

 fulcrum is elevated, and the rami depressed, so that the former 

 is invisible ; the rami open and shut with the working of the 

 mallei, being fastened to them by the strong triangular muscle 

 above mentioned. . . . It is also evident that they have a mo- 

 tion of separating and closing independent of the mallei, 

 though this is comparatively limited in extent, and not very 

 often exercised. Again, when substances are brought into 



