122 ROTIFERA [CH. 



of isolated bands, chiefly longitudinal, which retract the disc and 

 the foot and bend the body in various ways, the recovery of its 

 original shape being due largely to the elasticity of the cuticle. 



The food, which consists of Protozoa and other small organisms, 

 is swept into the mouth by the action of the surrounding cilia. 

 The mouth leads through a wide vestibule into an oesophagus, 

 which is ciliated and projects down into the so-called gizzard or 

 mastax which, next to the ciliary rings on the head, is the most 

 characteristic organ of a Rotifer. The vestibule, oesophagus and 

 mastax are all part of the stomodaeum. The cuticle lining the 

 mastax is thickened so as to produce the trophi, which are hard, 

 chitinous, chewing organs ; of these there are typically three, two 

 mallei and an incus on which they strike. The incus, a Y-shaped 

 piece, consists of two rami and a central piece or fulcrum. Each 

 malleus is composed of a manubrium and an uncus or head, 

 which may be toothed. The shape and arrangement of these hard 

 parts is of great value in classification. In some species the mallei 

 are absent altogether, and the two rami of the incus then work 

 against one another like two lateral teeth. In the NOTOMMATIDAE 

 the mallei can be protruded through the mouth and are used to 

 cut into the cells of Algae on which the animals browse. In 

 Floscularia and its allies there is a dilatation of the stomodaeum, 

 called the crop, interposed between the mastax and the oeso- 

 phagus, and the latter hangs down into the crop just as a funnel 

 might hang into a tumbler: the crop can be everted through the 

 mouth. 



After passing between the jaws the food enters the stomach, 

 which is lined with cilia; here the food loses its original colour 

 and becomes tinged with the brown secretion of the walls of the 

 stomach. In most forms two salivary glands open into the mastax 

 and two gastric glands into the stomach, but these have not been 

 clearly made out in Floscularia,. The stomach is separated by a 

 constriction from the ciliated rectum, and this ends in a non-ciliated 

 tube into which the genital and excretory organs also open. This 

 tube consists of ectoderm turned in at the anus and is therefore 

 termed the proctodaeum (Gr. TT/DCOKTO'S, anus), a word formed on 

 the analogy of stomodaeum. The alimentary canal of Rotifera, 

 like that of the lower Vertebrata, thus terminates in a cloaca, 

 that is to say in a tube which is a common channel for all the 

 products which have to be expelled from the body. The word 

 cloaca it is hardly necessary to remind the reader was originally 

 applied to the great main sewer of ancient Rome. 



