440 ROTIFERA. 



(1137.) After passing the dental organs, the food enters an elongated 

 stomach (fig. 227, 1, /) with very thick pulpy parietes. In young 

 examples these walls are colourless and transparent, but in more ma- 

 tured specimens they exhibit a bright-olive hue. The whole cavity, as 

 well as the oesophagus leading to it, is lined with cilia that are con- 

 stantly playing. On rupturing this organ, it is seen to be composed of a 

 thin pellucid external membrane, exhibiting no distinct structure, but 

 within which is a thick layer of large, tinged epithelial cells. These 

 are easily detached from the membrane, when each one is seen to be 

 spherical, containing numerous yellow granules, and very often a nucleus 

 with its nucleolus. The cilia are attached to one side of these cells, 

 the great length of the former constituting the most marked feature of 

 this arrangement; it often, indeed, equals the entire diameter of the 

 cell. Some of the cells exhibit no cilia, others are only furnished with 

 them on one side, while a few appear to be fringed with them through- 

 out their entire circumference. Professor Williamson supposes that in 

 the latter case the cells have projected considerably into the cavity of 

 the stomach. The yellow granules are absent from those of young 

 animals, showing clearly that it is these contained granules that give 

 the colour to the parietes of the stomach. 



(1138.) This stomach appears to be chiefly a receptacle for the food. 

 From time to time, especially when the viscus is distended, portions 

 of its contents pass down into a lower stomach (fig. 227, 1, #), which 

 is separated from the upper one by a marked but varying constriction. 

 The second stomach is also lined with cilia even larger than those of the 

 upper viscus ; but the parietes are very much thinner and more trans- 

 parent, the cells being less easily traced. The diameter of the organ is 

 nearly the same in each direction, so that it is almost spherical. The 

 mass of food with which it is usually distended is constantly revolving, 

 the motion being due to ciliary action. This process goes on for some 

 minutes, after which the creature contracts its body and forces the en- 

 tire contents out of this viscus into a long narrow cloaca that terminates 

 externally by an anal outlet (fig. 227, 1, h). As it does this, it everts 

 a considerable portion of the cloaca, thus almost bringing the cloacal 

 outlet of the stomach to the exterior, and causing at the same time a 

 large transparent protuberance (fig. 227, 1, i) to be developed on the 

 corresponding side of its body. At other times the creature can draw 

 in these appendages, so that scarcely any trace of a cloacal canal is 

 visible. 



(1139.) Notwithstanding the microscopic size of the Rotifera, and 

 the consequent difficulty of detecting the more minute details of their 

 structure, Ehrenberg thinks he has succeeded in discovering filamentary 

 nerves, and nervous masses, distributed in different parts of their body, 

 an arrangement which not only would account for the complete asso- 

 ciation of their voluntary movements, but, from the presence of ganglia, 



