WHEEL-BEAREBS. 253 



until the mass was discharged just behind the sinuous 

 cleft. On our mixing carmirie 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 Brachionus, and yet essentially it is 

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

 tive 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 



