Male Sexual Organs ? of the Infusoria, 45 



which they also assume. Whilst the mouth is open, monadina of 

 a considerable size can easily pass between the teeth down into 

 the stomach, but the narrowing of a dental cylinder at the bot- 

 tom of the mouth does not allow them to come out again so 

 easily, even if the mouth be open. Perhaps the contractions 

 which are sometimes remarked at the anterior part of the cylin- 

 der, apparently without any distinct object, are the result of 

 the sensation which the animal experiences at the bottom of 

 the mouth, when the animalcules it has swallowed endeavour in 

 this way to make their escape. 



Finally, it may be observed, that, on one occasion, when M. 

 Ehrenberg was dividing a Nassula ornata and a N. elegans, he 

 observed the existence of a second and new dental apparatus; 

 and that, in an individual of the first species, he observed an ir- 

 regularity in the original one which appeared to be preparatory 

 to a longitudinal division of the teeth. The regeneration of the 

 whole teeth of the mouth, a phenomenon trujy rare in the animal 

 series, is very common among the Infusoria, with whom a ten- 

 dency exists to multiply, by a spontaneous division. The In- 

 fusoria lacera, as soon as the posterior portion is separated from 

 the rest of the body, produces afresh a new anterior portion, 

 provided with a mouth, teeth, &c. M. Ehrenberg mentions his 

 having seen a great number of Infusoria of a primary or nor- 

 mal formation, which he had examined during the day, divide 

 themselves transversely during the following night, and, next 

 morning, all the posterior parts had each produced a mouth full 

 of teeth, which were perfectly organized. Many others were 

 not entirely divided into two parts : he gave an unremitting at- 

 tention to these, and found that the development of the parts 

 for a time deficient made the most rapid progress ; to such an 

 extent, that he calculated that the whole of the division, and 

 the formation of twenty teeth, might be effected in the space of 

 two hours. (See PI. I. fig. 2.) 



II. Concerning a System of Internal Organs y simple, double, or mul- 

 tiple, very irritable, which may be discovered in the Polygastrica, 

 and which, perhaps, are the male Sexual Organs. 



Though Professor Ehrenberg had very often minutely exa- 

 mined the Paramecium aurelia, one of the best known Infu- 



