POLYGASTRIA. 27 



On the 20th No. 1. had propagated five individuals by transverse 

 spontaneous division : in No. 4. eight individuals had in like manner 

 been generated. 



On the 21st no change had taken place. 



On the 22d there were six nearly equal-sized individuals in No. 1., 

 and eighteen individuals in No. 4. 



On the 23d, the individuals were too numerous to be counted. 



Thus it was demonstrated that this species of Polygastrian would 

 continue for six days without any diminution of reproductive force, 

 and that on one day a single individual twice divided, and one of its 

 divisions effected a third fission. 



A similar experiment on a Stylonycliia Mytilus, an animalcule one 

 tenth of a line in length, was attended with nearly the same results ; 

 it was supplied with the green nutrient matter, consisting of the 

 Monas pulvisculus, and on the fifth day the individvials generated by 

 successive divisions were too numerous to be counted. 



And now yovi may be disposed to ask : To what end is this discourse 

 on the anatomy of beings too minute for ordinary vision, and of 

 whose very existence we should be ignorant unless it were revealed 

 to us by a powerful microscope ? What part in nature can such 

 apparently insignificant animalcules play, that can in any way interest 

 us in their organisation, or re^jay us for the pains of acquiring a know- 

 ledge of it ? I shall endeavour briefly to answer these questions. 

 The Polygastric Infusoria, notwithstanding their extreme minuteness, 

 take a great share in important offices of the economy of nature, on 

 which our own well-being more or less immediately depends. 



Consider their incredible numbers, their universal distribution, 

 their insatiable voracity ; and that it is the particles of decaying 

 vegetable and animal bodies which they are appointed to devour and 

 assimilate. 



Surely we must in some degree be indebted to those ever active 

 invisible scavengers for the salubrity of our atmosphere. Nor is 

 this all : they perform a still more important office, in preventing the 

 gradual diminution of the present amount of organised matter upon 

 the earth. For when this matter is dissolved or suspended in water, 

 in that state of comminution and decay which immediately precedes 

 its final decomposition into the elementary gases, and its consequent 

 return from the organic to the inorganic world, these Avakeful 

 members of nature's invisible police are every where ready to ar- 

 rest the fugitive organised particles, and turn them back into the 

 ascending stream of animal life. Having converted the dead and 

 decomposing particles into their own living tissues, they themselves 

 become the food of larger Infusoria, as the Rotifcra, and of numerous 



