OF THE MANDUCATORY ORGANS IN THE CLASS ROTIFERA. 
437 
ordinary form of a chamber inclosing^ the trophi. The fulcrum is attached to a reni- 
form muscular cushion (fig. 56) ; with the rami projecting freely into the huccal funnel ; 
and, under graduated pressure, protruded from the front, when they snap vigorously. 
But when we consider that the normal form of the mastax is that of three lobes, of 
whieh one belongs to the incus, and two to the mallei, it is natural to expect that 
the evaneseence of the mallei would be accompanied by the evanescence of their 
muscular lobes. And this I conclude is the true state of the case: the cushion is 
the lobe of the incus, and therefore the sole representative of the mastax ; the lateral 
lobes having become obsolete. 
88. I was unwilling to interrupt the regular gradation, through which we have 
traced the degeneration of the mallei to evanescence ; but I now retrace my course 
a little, to notice how the same organs degenerate in other modes. In a beautiful 
and common species, well known to most microscopists, Mastigocerca carinata (figs. 
60 to 62), the dental apparatus occurs under an unusual form. The mastax is a 
somewhat slender sac, much produced in length, and with the component lobes 
greatly and irregularly developed. The incus has a fulcrum of great length and 
slenderness, a straight rod with a dilated foot (fig. 62, h). The rami are small, 
forcipate, and resembling those I have lately described ; but with the alulce greatly 
produced (o). The mallei have long, slender, incurved manuhria, and simple unci. 
89. But the remarkable circumstance is the non-sym metrical character of the 
apparatus. The left side is much more developed than the right. The left alula of 
the incus (o) descends to a greater distance than the right (o') ; and its extremity is 
dilated into an expansion, with several irregular angles, to which muscular threads 
are attached. The ramus also of the same side is larger than its fellow. So with 
the mallei. The manubrium of the right (o') is comparatively short, very slender, and 
of uniform thickness; with a long, slender, rod like uncus (e'), doubly bent in the 
middle, 'fhe left is much longer, irregularly swollen, clubbed at the articulation, 
and bearing a thick, curved, knobbed uncus, which terminates at a point not precisely 
opposite the tip of its fellow (e)*. 
90. In Monocerca (fig. 63), — from which Mastigocerca can scarcely be said to differ 
generically, though Professor Ehrenberg places it in another family, — the right 
malleus entirely disappears, not a vestige of it remaining ; though the left {h) is long, 
and well developed. The incus is a straight rod, with a high carina (/*), with the 
rami almost obliterated : the alulce, however, are rather large, but unequal. 
91. This want of symmetry is a remarkable character of the genus, and is dis- 
played in other particulars. For example, in. Monocerca bicornis, the little projecting 
tubular organ, which Ehrenberg has called the respiratory tube, but which I con- 
sider a rudimentary antenna, is double ; but the two are unequal. In the same 
species, and also in M. porcellus, the lorica terminates frontally in two spines, of 
* In Notommata parasita there is a similar want of symmetry, the right manuhrium, being much shorter than 
the left (see my memoir in Trans. Micr. Soc. iii. p. 143). 
3 M 2 
