44« M. Ehrenberg's Researches on the Infusoria, 



teeth of the Hotatoria, which, in their turn, present a close ana- 

 logy to those of the Entomostracea (Daphnia, Cyclops). In 

 pressing the animal between two plates of glass, so as to bruise 

 the soft parts, the teeth remain, and are very distinctly visible, 

 which proves that they are more solid than the other parts. 



The number of teeth isgreater in this class than in the Rotatoria. 

 None of the polygastric infusores which possess them have less 

 than 16 ; and, in the larger, as, for example, in the Prorodon com- 

 pressus, more than 30 have been discovered. Professor Ehren- 

 berg has in many instances given the precise number. Thus, 

 Eiiodon cucullulus has 16; the Nassula ornata S6 ; the N, ele- 

 gans 22; the N. aurea'W ; and the Prorodon niveus has more 

 than 20. The extreme minuteness of these teeth, and their posi- 

 tion in very close cylindrical groups, very much increases the dif- 

 ficulty of observation, and especially that of the determination of 

 the number, which, indeed, cannot be done, except when the 

 animal is so placed that the opening of the mouth directly faces 

 the observer. In all other positions, he can see but a part of 

 the teeth, because there are always some which are covered by 

 the others. 



The pharynx of these Infusoria has less play in the act of 

 deglutition in this class than in the Rotatoria. It often hap- 

 pens, that when the animal is vibrating its rotatory cilia, it 

 leaves its mouth open, and without action, and then the nou- 

 rishment which happens to be drawn in, enters into the cavity 

 indifferently, and the animal does not move its jaw at all. Biit 

 when the little creature wishes to swallow larger morsels, then 

 it previously masticates them. In this case, the buccal cylinder 

 first enlarges itself at its orifice for the reception of the nourish- 

 ment ; at that time it is narrow farther down, but as the morsel 

 proceeds, it contracts behind, and dilates before it. During this 

 movement, the mouth itself is often quite shut ; nor is it rare to 

 witness all these movements executed, when no large morsel at 

 least has been taken. 



An essential difference between the teeth of rotatory and po- 

 lygastric animals consists in this, — that in the first they are at- 

 tached to the bottom of the mouth on the pharynx, and act la- 

 terally one upon the other ; whilst, in the Polygastrica, they 

 rather resemble in their arrangement a purse-net, the form of 



