Nucleus of the Animal and Vegetable " Cell.^^ 207 



is transformed into a layer or brood of cells, its place is 

 taken by the enlarging nucleolus ; which again is succeeded 

 by a fresh nucleolus, arising in the centre from which the 

 former had enlarged. Compare with a cell in the woodcut 

 fig. 26, and with a corresponding cell in fig. 39 of Plate I. 



And this process, it will be seen, begins before the com- 

 plete formation of even Schleiden's cytoblast. See figs. 2, 3. 



The membrane of the nucleus or cytoblast, becoming the 

 inner cell in fig. 8, and represented in all the succeeding 

 figures, — though distinct enough, capacious, and for some 

 important ^nr^o^e filled with pellucid fluid' when in a central 

 situation^ (Plate I., fig. 45 /3), — is rarely seen with distinct- 

 ness when subsequently pushed out from the centre by a 

 fresh brood, and made to separate two layers of cells : and 

 often it entirely disappears, as shewn by several bodies in 

 fig. 39, Plate I. 



I have just spoken of the cell-membrane, as formed by 

 minute globules. An immeasurably minute cell-formation, 

 however, seems even here to intervene. Fig. 38 in the Plate 

 presents part of the membrane of a very important cell pro- 

 duced by the coalescence of minuter cells, the formation of 

 which it is not difiicult to follow.* And you afterwards find 

 in its substance the nuclei, or germinal centres, of the cells 

 which formed it (see the figure). Yet so very small is that 

 cell at first, that two hundred millions of them could be con- 

 tained in a cubic inch. To that cell (my ovisac-^) I shall pre- 

 sently return. I wish now to add, that there is thus a con- 

 siderable difference between my views and those of the Ger- 

 man physiologists just mentioijed, as to the mode of origin 

 not only of the cytoblast, but of the membrane of the cell. 

 The substance of the larger body is not deposited around the 

 the smaller, but the smaller is transformed into the larger. 

 The nucleolus becomes a cytoblast, and the cytoblast becomes 

 a nucleated cell. 



From the foregoing remarks and figures it will also be 



* See in Phil. Trans., 1841, Plate xxV., figs. 170, 171, 172, 173. 

 t Phil- Trans., 1838. 



