ANIMAL NATURK OF DIATOMH^E. 357 



wall is not only enlarged, but successively impregnated 

 with various substances, as lignine (C.-"^ H.^° 0.'), with 

 carbonate of lime, with silica, or, finally, with a quaternary 

 azotised substance, as constantly happens in a portion of 

 the superior wall of the epidermal cells which forms tlio 

 so-called cuticle, and in the thick cellular wall of marine 

 Confervse. Thus the elongation effected in animal cells, 

 on their nuclei and on their nucleole passing into distinct 

 fibres, has only a remote counterpart in the liber cells of 

 plants, in the hypothalline tissue ofLichens, in the so called 

 seminal threads of Charse and Musci, and in some modifi- 

 cations of Kiitzing's amylide cells. But these fibres, 

 so distinct in the superior animals, and in many of 

 the inferior, as in Sponges, for example, entirely elude 

 observation when we examine microscopic beings. 



In animals, as well as in plants, new cells are 

 organised in the interior of their predecessors ; but in 

 vegetables the formation of the cells always seems to be 

 endogenous; in animals, on the other hand, it takes 

 place perhaps usually in the extra cellular fluid. The 

 multiplication of vegetable cells is proved to occur in 

 three modes. 



1 . Many nuclei appear floating together with granules 

 of a different nature. Around each of these collects a 

 minute vesicle, which successively increases, compresses 

 the whole of them, and, along with them, terminates by 

 filling the maternal cell, which, softening and liquefying, 

 is finally absorbed and disappears. 



2. The internal substance of the cell divides into 

 two or four portions, which, from their origin, are seen 

 to be surrounded by a distinct primitive fine membrane 

 and each to be furnished with its respective nucleus, 

 whilst the primitive nucleus and membrane of the ma- 

 ternal cell disappear. And, consequently, only one or 

 two diaphragms divide the cavity among them, and, 

 by detaching themselves, constitute the walls of the new 

 cells. 



3. In the third mode of cellular multiplication it is 



