358 ANIMAL NATURE OF DIATOME^E. 



the wall itself of the maternal cell that, by inflecting itself 

 into an annular fold, constricts the fine primitive mem- 

 brane, which in such a case is persistent, and divides it 

 into two portions, so that on arriving at the centre, it 

 completes the diaphragm. 



In the animals there have hitherto only been observed 

 with exactness the first two modes of endogenous forma- 

 tion of cells. 



If now we descend from the comparative examination 

 of the vegetable and animal cell, considered generally, to 

 the special examination of the more simple organisms 

 among vegetables, excluding all those that can be con- 

 sidered of an ambiguous nature, we shall find almost 

 countless numbers which present in perfect clearness, 

 and in their primitive as well as in their permanent state, 

 the most simple condition of a cell and its successive 

 changes. 



Among animals, on the other hand, we certainly have, 

 as a primordial and transitory state, the egg or ovum, 

 especially in the lower animals, which are very convenient 

 for observation ; but as representatives of their permanent 

 state reduced to its extreme simplicity, we possess solely 

 the genus Gregarina, of which we know six distinct 

 species, all of them Entozoa, all organised as simple cells, 

 but endowed at the same time with contractility and 

 expansibility quite sufficiently to put their animal nature 

 beyond doubt. For, when we consider the more simple 

 Infusoria, the Monades, the Vibriones, and Paramecia, 

 we soon perceive that their simplicity is apparent only. 

 In respect to these (Monades, &c.) we have not to take 

 merely account of properties inherent in a simple cell, 

 but must rather seek to estimate those which belong to 

 tissues whose organic elements escape our sight. Che- 

 mical reagents exert only a complex action upon the 

 entire material of the body, whence we suppose it to 

 be principally constituted of an azotised substance. 

 And here I dwell upon the peculiarities of such Infusoria ; 

 for if, on one hand, they denote an organisation far more 



