422 MR. P. H. GOSSE ON THE STRUCTURE, FUNCTIONS, AND HOMOLOGIES 
tms, or a lateral one in Furcularia : but when we have done this, we have gone but a 
little way towards such an understanding of the whole form, and the relation of the 
complex parts to each other, as will enable us to project them, or to form an ideal 
model of the whole. A little more light is shed on the structure by crushing the 
animals between plates of glass, or under the graduated pressure of a compressorium; 
but the distortion of the parts is very great ; and some of them, especially those which 
form the intermediate piece {incus), on which the greatest obscurity rests, are almost 
invariably broken into a multitude of separate fragments in the process of flattening ; 
and thus the result merely tantalizes the expectation. 
11. Little more seems to be yet known of the structure of the manducatory organs 
(I speak of the normal forms) than can be obtained by these modes, and the pub- 
lished descriptions of them are vague and unsatisfactory. 
12. Thus Ehrenberg describes the general structure as follows: — “The normal 
intestinal canal in the Rotifera consists first of a globose muscular throat-bulb 
(schlundkopf), in which are fixed two toothed jaws, and the anterior opening of which 
is placed in the midst of the wheel-organ, somewhat towards the belly [side]*.” — 
“ In all the forms there is a moving manducatory organ (kauorgan), furnished, in 
forty-eight genera, with indubitable teeth, and evidently ministering to the aliment- 
ary canal 'f'.” 
Again, in proposing a division of the class, according to the teeth, he groups the 
Rotifera as, i. Toothless {Agomphia) ; ii. Free-toothed {Gymnogomphia), where the 
teeth resemble the fingers of a hand fastened to the jaw-frame behind, but free in 
front ; iii. Bound-toothed (Desmogomphia), where the teeth are fastened across upon 
the jaw, like an arrow upon a bow 
The most laboured description of the normal structure the same zoologist has 
given under the genus Hydatina, which he professedly makes the vehicle for ardsfini^ 
of his acquaintance with the typical forms of the class. “ The nutritive system,” he 
observes, “ consists of a great buccal cavity, chiefly enclosed and formed by the rota- 
tory organ, as an upper lip ; in the bottom of which, near the ventral side, lies the 
spherical four-muscled throat-bulb, with two many-toothed jaws. In each jaw are 
held five conical teeth, resembling a hand, somewhat converging towards the bot- 
tom, diminishing in size inwardly. Sometimes a minute sixth tooth appears to be 
developed. The five teeth of each jaw, which are perceived, on crushing the body 
between glass plates, to be the only hard and solid parts, are jointed into a cartila- 
ginous frame, which serves for the attachment of the muscles, and has the form of a 
shoulder-blade. This is the proper jaw, which is composed of several parts. In- 
wardly, both jaws are in connexion with a frame of cartilaginous throat-arches, 
which is very complicated, and seems more fitted for the support and attachment of 
the masticatory muscles than for proper activity §.” 
13. I sliall presently show that these descriptions are both very imperfect and very 
* Trans. Berl. Acad. 1830, p. 29. f Infusionsth. p. 385. + Ibid. p. 386. § Ibid. p. 414. 
