380 M. Coste on the Formation of Cells. 



tible of playing a more or less active part in the organization of 

 plants. But this mode of formation of the walls of the cells not 

 being the only one observed by M. Mirbel, this physiologist has 

 been induced to admit, that in vegetables nature attains her ob- 

 ject by different means. 



However, this manner of viewing and judging of the phseno- 

 mena of which the cambium is the seat was soon accompanied by a 

 diametrically opposite system, the exclusive foundation of which 

 does not admit of the possibility of an exception. This system, 

 contrived by Schleiden to explain the formation of the vegetable 

 tissue, and applied by Schwann to the organization of animals, as 

 we shall presently see, is essentially no more than a generalization 

 a priori of Purkinje's theory of the development of the egg in 

 the ovary, — a theory, a large part of which has unfortunately lost 

 much of its value from new discoveries which have diminished 

 its importance, or even reduced it to the level of the most rare 

 exceptions. 



Purkinje, after having recognised that the germinal vesicle, 

 among all the component parts of the bird^s egg, was that which 

 from its origin had a proportionately more considerable develop- 

 ment, supposed that it was first formed, and considered it as a 

 centre around which were successively deposited, first the vitellus, 

 and then the vitelline membrane, which, in its turn, coagulated 

 at the periphery of the yolk to complete the ovarian egg, and to 

 inclose its elements in an enveloping membrane. This successive 

 union of concentric parts, mechanically superadded around each 

 other, so that the most external are the most recent, having ap- 

 peared to Schleiden and Schwann the most simple means of con- 

 ceiving the formation of the vesicular walls, these naturalists 

 formed it into a general theory of the development of the cell ; 

 and with them the enunciation of the special fact, modified as we 

 shall presently show, has become the foundation of a universal 

 principle. 



Consequently they admitted, that in the diffuse and structure- 

 less homogeneous substance, the cytoblastema, by means of a 

 concentration of this substance, corpuscles were formed; these 

 were so extremely minute, that even the highest powers of the 

 microscope did not allow of their always being detected. These 

 corpuscles, called nucleoli, are so many centres around each of 

 which a layer of finely-granular matter is deposited, which is not 

 at first distinctly limited in its circumference, but which finally 

 becomes more clearly outlined, and forms more or less regularly 

 spheroidal, elliptical or lenticular agglomerations. 



Each of these minute accumulations of amorphous matter 

 around one or even several nucleoli^ which they unite, is called 

 a cytoblast or nucleics, and forms the second phase of the process 



