OF THE MANDUCATORY ORGANS IN THE CLASS ROTIFERA. 
447 
looking- towards the Polyzoa ; whereas, it is in the highest forms that we must expect 
to find affinities with the Arthropoda. 
137. To the Arthropoda I am convinced that the Rotifera belong — the humblest 
members of that great group ; though, as my present business is with one system 
of organs alone, I am precluded, at this time, from adducing the various reasons 
derived from other parts of their economy, which have guided me to this conviction. 
I think that they lead, however, to the Insecta rather than to the Crustacea. 
138. The dental organs in Rotifera are true mandibulce and maxillae, and the 
mastax is a mouth. This is a startling proposition, if we look only at Floscularia, 
where it is situated in the midst of the abdominal cavity, or at the Philodinadce, and 
the Brachionidce, where it is enclosed in the breast. But I have shown that the 
apparatus is identical, in these families, with that of Diglena, Furcularia, and Synchoeta, 
in which it is terminal and protrusile. And this latter is the normal condition. I 
have myself witnessed the protrusion of the jaws from the surface of the body, in the 
following genera : — Furcularia, Pleurotrocha, Taphrocampa, Notommata clavulata, 
N. aurita, N. petromyzon, N. parasita (all of which represent different genera), Pla- 
giognatha, Scaridium, Synchoeta, Polyarthra, Diglena, Asplanchna, Mastigocerca, 
Monocerca, Salpina, Monostyla, and Anurcea. 
139. The integument in the Rotifera is very flexible, and, especially in the 
frontal regions, is extremely invertible. In those genera in which the buccal appa- 
ratus can be brought into contact with the external water, it is ordinarily, to a 
greater or less degree, retracted within the body, by the inversion of the surrounding 
parts of the exterior ; while, in those genera in which it is permanently enclosed, 
analogy requires us to consider this condition as induced by a similar inversion, but 
of permanent duration. If we imagine the head of a soft-bodied Insect -larva retracted 
to a great degree (as is done partially by many Dipterous larvae), the skin of the 
thoracic segments would meet together in front, around a purse-like opening, which 
would be the orifice of such a buccal funnel as exists in most Rotifera. In the 
latter, it is the normal condition ; in the former, it is merely accidental. 
140. The delicacy and transparency of the mastax are, indeed, unlike the corneous 
and opaque mouths of Insects, and of most larvae ; but its walls are composed of the 
same solid materials as the teeth themselves ; since they are left after treatment with 
potash, which dissolves away the muscles*. 
141. There is, then, no difficulty, I think, in identifying the mallei with the man- 
dibles, and the rami of the incus with the maxillae, of Insects. Perhaps the unci of 
the former more strictly represent the mandibles themselves, and the manubria the 
* “ In many Dipterous insects the head is covered with the same flexible membranous skin with the rest of 
the body, from which it is often scarcely to be distinguished. In these, except that it contains the organs of 
mandueation, it wears no more the appearance of a head than any other segment of the body. The head of 
these larvse is also remarkable for another peculiarity ; that it is capable of being extended or contracted, and 
of assuming different forms at the will of the insect” (Kirby and Spence, Int. to Ent. iii. 113). 
