252 THE CELL-THEORY 



same fashion. The Hmbs of animals, he says, are developed in the 

 same manner from the body of the embryo, as the leaf from the stem, 

 ■or the lamina of the leaf from its mid-rib. Ordinary four-footed 

 animals are like pinnatifid leaves, while " the bat is a perfect leaf — a 

 startling statement, but, as I have shown, the analogy is not chimerical 

 for the mode of origin of the two is the same!' ^ 



Wolff's doctrine concerning histological development is shortly 

 this. 2 Every organ, he says, is composed at first of a little mass of 

 clear, viscous, nutritive fluid, which possesses no organization of any 

 kind, but is at most composed of globules. In this semi-fluid mass, 

 cavities {Bldschen, Zelleji) are now developed ; these; if they remain 

 rounded or polygonal, become the subsequent cells — if they elongate, 

 the vessels ; and the process is identically the same, whether it is 

 examined in the vegetating point of a plant, or in the young budding 

 organs of an animal. Both cells and vessels may subsequently be 

 thickened, by deposits from the " solidescible" nutritive fluid. In 

 the plant, the cells at first communicate, but subsequently become 

 separated from one another ; in the animal, they always remain in 

 communication. In each case, they are mere cavities, and not indepen- 

 dent entities ; organization is not effected by them, but they are the 

 visible results of the action of the organizing power inherent in the 

 living mass, or what Wolff calls the vis essentialis. For him, however, 

 this "vis essentialis" is no mythical archtzus, but simply a convenient 

 name for two facts which he takes a great deal of trouble to demon- 

 strate ; the first, the existence in living tissues (before any passages 

 are developed in them) of currents of the nutritious fluid determined 

 to particular parts by some power which is independent of all external 

 influence ; and the second, the peculiar changes of form and composi- 

 tion, which take place in the same manner. 



Now there is really no very great difference between these views of 

 the mode of development of the tissues and those of Schleiden 

 and Schwann. The " solidescible nutritive fluid " of Wolff is the 

 " cytoblastema " of Schleiden and Schwann ; with the exception of 

 the supposed relation of the nucleus to the development of the cell 

 (which, as we shall see, is incorrect) Wolffs description of the latter 

 process is nearly that of Schleiden ; Wolff maintains that the "vessels " 

 of plants are the result of the greater activity of the nutritive currents 

 in particular directions ; and so does Schleiden.^ 



' Theorie von der Generation, § 64. 



Theoria Generationis, and Von der eigenthiimlichen Kraft, p. 48. 

 ^ It is very curious to find even Schwann's definition of cell-development as the " crystal- 

 lization of a permeable body" ^anticipated by Wolff, Von d. eigenthiimlichen Kraft, &c. , 



