412 



ROTIFERA. 



fig. 291.6). To the semicircular pieces are 

 attached some of the longitudinal muscles, 

 which, by their action, cause the teeth to work 

 upon the central plate. The general structure 

 of the jaws is, in all instances, the same, but 

 the number of processes, called teeth, varies 

 considerably. (Sometimes no such processes 

 are discoverable, as mCyphonautes ; in others, 

 there is but one tooth on each side, as in spe- 

 cies of Synchcsta, Diglena, Lepadella, and Mo- 

 nostyla. Some have two on each side, as Mo- 

 nocerca, Mastigocerca, and Rotifer (fig. 301.). 

 Others, again, present three, four, or several 

 teeth on each side, as in Brachionus brevisti- 

 mus (J%.300.), Triarthra longiseta (Jig. 297.), 

 Brachionus pala (fig. 296.). Such are the cha- 

 racters afforded by the teeth in this family, 

 that Ehrenberg gives an arrangement of the 



Fig. 301. 



Rotatory organs of Rotifer vulgaris enlarged. 



(After Ehrenberg.) 



a, hornlike process (respiratory tube) ; b, b, 

 muscles of tiie jaws ; c, c, intestinal glands. 



genera into orders, according to the absence 

 or presence and number of the teeth, as 

 follows : 



1. AGOMPHIA. Rotifers without teeth. 

 Examples : Chatonotus, Enteroplea. 



2. MONOGOMPHIA. With a single tooth. 

 Examples : Pleurotrocha, Furcularia. 



3. POLYGOMPHIA. With many teeth. Ex- 

 amples : Hydatina, Stephanoceros, Brachionus. 



4. ZYGOGOMPHIA. With double teeth. 

 Examples: Rotifer, Philodinee. 



5. LOCHOGOMPHIA. With teeth in rows. 

 Examples : Ptygura, Megalotrocha. 



The teeth seem to form the most dense 

 part of the body of the Rotifera, and, after 

 the crushing of the animalcule, may be ob- 

 tained for separate examination under the 

 microscope. 



The whole masticatory apparatus is at- 

 tached to the upper part of the alimentary 

 canal, the oesophageal head, where it may be 

 observed, being constantly in motion. This 

 movement, which goes on whether the animal 

 is partaking food or not, was mistaken by the 



earlier observers for the action of a heart. 

 Although, in most instances, the food is 

 brought to the jaws of the animal by the 

 rotatory apparatus, yet we have often ob- 

 served, in species of Brachionus, that they 

 have the power of projecting their jaws be- 

 yond the margin of the tegumentary mem- 

 brane, and bringing them immediately in con- 

 tact with the substances on which they are 

 feeding. 



The form of the alimentary canal varies : it 

 is sometimes a simple tube, as in Dinocharis 

 paupera (fig. 302. 6). In many species, an 

 enlargement of the middle portion takes place 

 from constriction of the canal, above and 

 below, forming a kind of stomach, as in No- 

 tommata myrmeleo (fig. 303. c), Brachionus 

 pala (fig. 296.). Sometimes there are two en- 



Fig. 302. 



Dinocharis paupera. 



Back riew. 

 a, anal orifice ; b, alimentary canal. 



largements of the canal, as in Triarthra lon- 

 giseta (fig. 297.). When the enlargement takes 

 place below alone, as in Rotifer vulgaris 

 (fig. 299.), and Philodina roseola (fig. 295. d), 

 Ehrenberg calls this portion a rectum. Eh- 

 renberg points out the form of the alimentary 

 canal as a mode of dividing the Rotifera, as 

 follow : 



1. Trachelogastrica, those with a long sim- 

 ple alimentary canal. 



2. Ctelogastrica, with a short oesophagus 

 and an oblong conical alimentary canal, as in 

 Hydatina. 



3. Gasterodela, in which the alimentary 



