VIH MOVEMENTS DIGESTIVE ORGANS 2Op 



on putting it into Water, to discover Multitudes of minute reddish 

 Globules, which are indeed the Animals, and will soon change 

 their Appearance, in the Manner just now mentioned. . . . 



"A Couple of circular Bodies, armed with small Teeth like 

 those of the Balance-Wheel of a Watch, appear projecting 

 forwards beyond the Head, and extending sideways somewhat 

 wider than the Diameter thereof. They have very much the 

 Similitude of Wheels, and seem to turn round with a considerable 

 Degree of Velocity, by which Means a pretty rapid Current of 

 Water is brought from a great Distance to the very Mouth of 

 the Creature, who is thereby supplied with many little Animal- 

 cules and various Particles of Matter that the Waters are 

 furnished with. 



" As these Wlieels (for so from their Appearance I shall beg 

 Leave to call them) are every where excessively transparent, except 

 about their circular Eim or Edge on which the Cogs or Teeth 

 appear, it is very difficult to determine by what Contrivance they 

 are turned about, or what their real Figure is, though they seem 

 exactly to resemble Wheels moving round upon an Axis. . . . 



"As the Animal is capable of thrusting these Parts out, or 

 drawing them in, somewhat in the Way that Snails do their 

 Horns, the Figure of them is different in their several Degrees of 

 Extension and Contraction, or according to their Position to the 

 Eye of the Observer, whereby they not only appear in all the 

 various Forms before represented, but seem at certain Times as if 

 the circular Eim of the Wheel or Funnel were of some Thickness, 

 and had two Rows of Cogs or Teeth, one above and the other 

 below that Eim." 



Digestive Organs. The pharynx is usually a narrow ciliated 

 tube, which varies in length from genus to genus, but in no 

 other important point, save in Flosculariidae, where it assumes the 

 form of a crop, into which the mouth hangs freely down as a 

 narrow ciliated tube. At its lower end is an enlargement, the 

 mastax or gizzard. 1 This is a strong muscular sac containing 

 the trophi or hard chitinous chewing organs, with an antero- 



1 Gosse's account of the "Structure, Functions, and Homologics of the Mandu- 

 catory Organs in the Class Rotifera" (in Phil. Trans. 1856) remains as the most 

 complete anatomical account we have, though his attempt to identify these parts 

 with the modified limhs of the Arthropod month has met with no support from 

 subsequent workers. Gosse rendered these parts clearly visible by the use of 

 dilute caustic alkali. 



VOL. II P 



