TUBE-DWELLING ROTIFERS. 31 



animals and other organic materials collected from 

 tlie surrounding water. 



It seems almost like drawing on the imagination 

 to speak of jaws and strong teeth, &c., &c., in 

 creatures so small as to be only just discernible 

 with the aid of a pocket-lens. Yet it is no fancy 

 sketch ; nay, more, the organs of which we speak 

 are not only clearly distinguishable with the aid of 

 the microscope; but some of them, such as the 

 mastax of M. ringens, with its jaws and teeth, 

 have been dissected out and mounted on glass as 

 separate objects of interest. 



This mastax is a prominent feature in all the 

 Rotifer a, and at once attracts the observer's atten- 

 tion. It consists of three well-developed lobes, 

 or masses of muscle, two of which, with the teeth, 

 are seen to be working against each other, grinding 

 down the food on to the third, which forms a sort 

 of table. The food thus finely triturated is now 

 passed on to the digesting stomach or alimentary 

 canal, which is divided into several compartments, 

 each furnished with its appropriate secretions for 

 converting the food into the tissues of the animal 

 body, &c. In fact, all, or nearly all, the organs 



