48 M. Ehrenberg"'s Researches on the Infusoria. 



versely and longitudinally, in such a manner, that after this di- 

 vision, each quarter of the body preserves a central part. It is 

 especially the Paramecium aurelia above named, which often 

 presents this appearance. The Paramecium kolpoda presents two 

 contracting vesicles, but they areplaced near to each other, and near 

 also to the middle of the back. The Euodon cucidlulus has three 

 vesiclesj two of which are situate upon the two sides of the den- 

 tal cylinder, and the third in the posterior part of the body, 

 near the dilatation of the intestinal canal close to the vent. It 

 has been remarked, that this little animal also frequently divides 

 itself in both ways, that is to say, both longitudinally and trans- 

 versely. In some others a single vesicle is placed in the ante- 

 rior part of the body, in some it is in the middle, and in others 

 it is in the posterior part. 



The relative situation and the number of these organs often 

 differs in the different species of the same genus. Thus the 

 Bursaria vernalis exhibits two, whilst the B. leuca and the B. 

 Jlava possess only one, and the B, spirigera shews none con- 

 spicuously. M. Ehrenberg also remarked that he had often 

 unavailingly sought for the organ in many of these beings for a 

 very long while, but when once found it always appeared very dis- 

 tinctly. They often remain for a long time in a state of con- 

 traction, and they are then quite invisible ; so that observations 

 must be often and patiently repeated, and their non-existence 

 must not be admitted incautiously. 



We must also observe, that Professor Ehrenberg seems to 

 have made another important discovery in the organization of 

 these infusores, which consists in the presence of a round organ, 

 less transparent than those we have been just considering, and 

 which is placed near the central contractile vesicle. In the 

 Euodon cuculluhis this organ is of an oval shape, of a dull white 

 colour, of considerable size, and placed in the middle of the ab- 

 domen. A body in every respect analogous exists in all the in- 

 dividuals of the Nassula elegans. Its position is somewhat ob- 

 lique in these two species. In the Nassula ornata and the N, 

 aurea it appears more globular, and is equally near to a central 

 vesicle. In these our species he has distinctly perceived this or- 

 gan, and more recently in the Paramecium aurelia also. He suc- 

 ceeded in this by feeding the animal abundantly in some coloured 



