INFUSORTAT, ANTMALPULEg. 49 



Rnimalciile, into two or more individuals ; also, by tlio growth of 

 gemmules, or buds, upon the parent. These various modes of propa- 

 gation account for their almost incomprehensible increase of number 

 in a very short space of time, and which has often astonished 

 observers. 



In the genus Chsterimn, the curious formation of double gems has 

 been observed by Ehrenberg, and is figured in plate 1. fig- 67. That 

 obser^^er remarks, " The increase by spontaneous di\ision, is the 

 character which separates animals from plants. It is true that the 

 gemmation in plants, especially, in very simple cells, is at times very 

 similar to the di^vision in animals ; but this relates to the form, not 

 the formation. A vegetable cell, apparently capable of self-division, 

 produces one, or contemporaneously many exterior buds f gemma- J, 

 without any change in its interior. An animal which is capable of 

 diAT-sion, first doubles the inner organs, and subsequently decreases 

 exteriorly in size. Self-diA-ision proceeds from the interior towards 

 the exterior, firom the centre to the periphery; gemmation, which 

 also occurs in animals, proceeds from the exterior towards the 

 interior, and forms first a wart, which then gradually becomes 

 organized." — {Annals Nat. Hist. v. ii.) 



The importance of this power, so forcibly exhibited in the various 

 tribes of animalcules, is well shcAvn by the fact, that a creature, 

 iuA^sible to the naked eye, can, in the space of four days, give origin 

 to no less than 140 billions of beings; and as, fr-om the size, &c., of 

 the bodies, we can easily calculate that 40,000 millions of individuals 

 exist in a cubic inch of the polishing slate of Bilin, so 70 billions 

 must be necessary to form a cubic foot of the same staaicture. 



This difference in nature between self-division in vegetable cells, 

 and in the cell-like bodies of Pohjgastrica, above insisted upon by 

 Ehrenberg, is opi^osed to the result of some recent researches. Thus 

 Mohl and Henfrey state, that when a plant cell is about to undergo 

 fission, the inner mucilaginous layer of its wall — the primordial xdride 

 manifests a constriction in the future line of separation, which 

 presently evidences itself in the outer cell- wall, and progresses until 

 the di^dsion is complete. (See observations on self-division in the 

 Bacillaria, imder the sections Desmidiacea and Diatomacea in part III. 



In the Vorticellina, M. Dujardin recognizes the existence of repro- 



E 



