124 Prof. Ehrenberg on Fossil and Recent Infusoria. 



organization^ which after many years of observation have been 

 gradually established, could not be brought into doubt by a 

 single doubtful fact. The perfect organization of the wheel 

 animalcules had been established beyond all question. With 

 regard to Paramcccium Aurelia, this is one of those forms un- 

 favourable to such observations ; and it had been expressly 

 observed by me that I myself had not been able to recognise 

 the alimentary canal in all species of the various genera ; but 

 on the other hand it was quite evident in a very considerable 

 number of species and genera. I stated that in my present 

 work this subject had been treated of in detail, and that those 

 forms in which the relations are perfectly evident have been 

 purposely enumerated. Some of these forms I then exhibited in 

 the drawings, and concluded with the remarlc that the circular 

 motion observed by Prof. Jones had already been treated of 

 by others (for instance. Dr. Foeke), and had naturally been 

 frequently observed by myself. The great contractibility of 

 the body of the animalcule was, to less practised observers, 

 not seldom a cause of enigmatical phenomena, of which con- 

 tinued patient observation of the object would gradually bring 

 the explanation. Thus, at times, the intestinal canal of the 

 animalcule extends at the expense of the ventral sacs so far, 

 that it occupies the whole space of the body, and then the de- 

 voured substances, very similar to the ventral sacs, circulate 

 in the whole body. Yours, &c. 



London, Sept. 15, 1838. Ehrenberg. 



b — 



(0 1. (0 2. (x) 3. 



Ideal figures of Loxodes Bursaria in various states of the extension 



of the alimentary canal, and its inner circular motion, not of the 



ventral sacs, but of the contents of the sacs voided into the canal. 



a the mouth, h the alimentary canal, c ventral sacs, w anal aperture. 



