WHEEL-BEARERS. 



253 



the faecal matter driven rapidly upward as through a 

 canal, until the mass was discharged just behind the 

 sinuous cleft. On our mixing carmine with the water, the 

 effect is very striking; the particles, whirled round in two 

 circular vortices, are poured in an accumulated torrent 

 through the sinuosity, and over the elevation at the front 

 of the head. We presently perceive a slender line of 

 crimson passing down below the mastax, which indicates a 

 slender stomach-tube there ; and, after a while, a little ball 

 of the same pigment accumulates, and is seen resting a 

 little lower down. This, then, indicates the form and 

 position of the stomach; it must be a very slender canal, 

 terminating in a small rounded bag, at about one-third of 

 the distance from the mastax to the base of the tube. The 

 lengthened sac which you see is the ovary, from which the 

 eggs are discharged into the lower part of the case. 



WHEELS OF TUBE-WHEEL. 



The mouth needs a little explanation in detail. As 

 you see it, you probably discern little resemblance in its 

 parts to the same organ in Braclrionns, and yet essentially 

 it is formed of the very same parts; and as it is very 

 instructive to observe the modifications, in different 

 animals, of a common model of any particular organ, it 

 will be worth while to devote a few minutes' careful 

 observation to this structure before us, especially as it is 

 here seen with more than usual brilliancy and clearness. 



The mastax, then, which you see in the centre of the 



