xiv AUTHOR'S PREFACE. 



these observations of Duraortier, in as much as they regard the 

 tissue consisting of cells as the yelk and not the liver. (Bulletin 

 de TAcad. royale de Bruxelles, torn, v, No. 5.) 



Other instances of the resemblance in form between different 

 animal tissues and those of vegetables had already been 

 repeatedly pointed out. Thus it was frequently said, in refer- 

 ence to thickly-crowded animal cells, or even mere globules, 

 that they presented an appearance resembling vegetable cellu- 

 lar-tissue ; and Valentin (Nov. Act. N. C. xviii, P. 1, 96), 

 after describing the nucleus of the epidermal cells, states that 

 it reminded him of the nucleus which occurs in the vegetable 

 kingdom, in the cells of the epidermis, the pistil, &c. Nothing, 

 however, resulted from such comparisons, because they were 

 mere similarities in figure, between structures which present 

 the greatest variety of form. 



Schleiden instituted researches into the mode of development 

 of vegetable cells, which illustrated the process most excellently. 

 This admirable work appeared subsequently in the second part 

 of Muller's Archiv for 1838. He found, that in the forma- 

 tion of vegetable cells, small, sharply-defined granules are first 

 generated in a granulous substance, and around them the cell- 

 nuclei (cytoblasts) are formed, which appear like granulous 

 coagulations around the granules. The cytoblasts grow for a 

 certain time, and then a minute transparent vesicle rises upon 

 them, the young ceil, so that, in the first instance, it is placed 

 upon the cytoblast, like a watch-glass upon a watch. It then 

 becomes expanded by growth. Schleiden communicated the 

 results of his investigations to me, previous to their publication 

 in October, 1837. The resemblance in form, which the chorda 

 dorsalis, to which J. Miiller had already drawn attention, and 

 the branchial cartilage of the tadpole present to vegetable cells, 

 had previously struck me, but nothing resulted from it. The 

 discoveries of Schleiden, however, led to more extended re- 

 searches in another direction. 



