418 GENEEAL niSTOEY OF THE INErSOEIA. 



rapidly transmitting and not retaining the food, and terminating in a compa- 

 ratively short conical intestine, without a stomach dilatation, e. g. Icliihydium, 

 Chcetonotus. 



2. Ccelogastnca, Rotatoria with a very short gullet, a long conical in- 

 testine, and no stomach, e. g. Hydatina, Synchceta. 



3. Oasterodela, those Rotifers having an evidently developed stomach, or 

 a dilatation of the alimentary canal limited by a definite constriction, 

 e. g. Euclilanis, Bracliionus, LeixideUa, Biglena, &c. 



4. Tracliehcystica, with an indistinct gullet, but having a very long, fili- 

 form, small intestine, in which the food is detained, and also a large globular 

 intestine (rectum or cloaca) placed close to the discharging orifice, e. g. Rotifer, 

 Act'inurus, PMlodina. 



Subsequent independent observers have been able neither to recognize all 

 these distinct types of structure nor to admit their value. Leydig, in fact, 

 insists that the so-called " gasterodelous " type is the only one seen in Rota- 

 toria ; but, as just now stated, several authors admit the existence of a simple 

 conical or tapering alimentary tube, without dilatation or stomach, in several 

 of the class. 



The Tnwhelogastrica are represented only by beings which are now, by gene- 

 ral consent, excluded from the Rotifera. The termination of the intestine in 

 a dilated sac-like expansion, in which also the generative canals end, whence 

 its name, " cloaca,^' is the rale ; or, to use Ehrenberg's term, the majority of 

 the Rotatoria are Trachelocystica. 



The stomach dilatation, like the rest of the alimentary canal, is capable of 

 great expansion, by which its figui^e is considerably altered. Usually but 

 one gastric cavity has been described ; but in some species there is a second, 

 and Huxley, in his history of Lacinidaria (XXXVII. 19), describes three 

 portions or divisions between the gastric canal and the rectum, — the fii'st 

 with two pyriform sacs opening into it, the middle one frequently with several 

 short cellular caeca, and the lowest ^ith several cellular cseca projecting ex- 

 ternally, and clothed within with very long cilia. According to Prof. Wil- 

 liamson, the stomach of Mdkerta (XXXYII. 17) consists of an upper and 

 lower segment, separated the one from the other by a marked though vary- 

 ing constriction, — the upper stomach elongated, the lower almost spherical, 

 Mr. Gosse describes this same organization in Melicerta, but calls the upper 

 segment "a wide cylindrical stomach," and goes on to say that the food 

 passes from this into a globose intestine which ends in a slender but dila- 

 table rectum. 



A similar double organ is found in Fhscularia, Btephanoceros (XXXVII. 

 1/), and Tubicolaria. Moreover Ehrenberg noted a sac attached to the 

 stomach of Megcdotrocha, which he called a caecum. The configuration of 

 the stomach is otherwise altered by tubular and saccular appendages, and in 

 a few instances is lobular, as stated by Mr. Gosse in Asplancli^ia (XXXYI. 

 9 s). Ehi'enberg states, at p. 399 of his great work, that the stomach of 

 Lacinidaria is complicated by two blind tubes (intestines), and yet, at p. 403, 

 reverses this statement by saying that it is '' without bhnd intestine-hke ap- 

 pendices." Leydig admits the latter as the truth ; but, as already seen, 

 Huxley remarked two pyriform sacs attached to the first, and caeca to each 

 of the other two segments. Ehrenberg further describes caecal appendages to 

 the stomach of Notommata clavidata, and of Diglena Jamtstris, but such were 

 probably the turgid stomach-cells presently noticed. 



The tissues or histological elements entering into the formation of the 

 stomach are — 1, a limiting external membrane, and, 2, an internal layer of 

 epithelium (XL. 4). The former is the same tissue with that constituting 



