394 CELL-DIVISION AND DEVELOPMENT 



('94) found that in the regeneration of decapitated hydranths of tubu- 

 larians the new hydranth is primarily formed, not by new cell-formation 

 and growth from the cut end, but by direct transformation of the distal 

 portion of the stem.^ Morgan's remarkable observations on Planaria, 

 finally, show that here also, when the animal is cut into pieces, com- 

 plete animals are produced from these pieces, but only in small degree 

 through the formation of new tissue, and mainly by direct remould- 

 ing of the old material into a new body having the correct propor- 

 tions of the species. As Driesch has well said, it is as if a plan or 

 mould of the new little worm were first prepared and then the old 

 material were poured into it.^ 



Facts of this kind, of which a considerable store has been accumu- 

 lated, give strong ground for the view that cell-formation is subordi- 

 nate to growth, or rather to the general formative process of which 

 growth is an expression ; and they furnish a powerful argument against 

 Schwann's conception of the organism as a cell-composite (p. 58). 

 That conception is, however, not to be rejected in toto, but contains a 

 large element of truth ; for there are many cases in which cells pos- 

 sess so high a degree of independence that profound modifications 

 may occur in special regions through injury or disease, without affect- 

 ing the general equilibrium of the body. The most striking proof of 

 this lies in the fact that grafts or transplanted structures may perfectly 

 retain their specific character, though transferred to a different region 

 of the body, or even to another species. Nevertheless the facts of 

 regeneration prove that even in the adult the formative processes in 

 special parts are in many cases definitely correlated with the organi- 

 zation of the entire mass ; and there is reason to conclude that such 

 a correlation is a survival, in the adult, of a condition characteristic 

 of the embryonic stages, and that the independence of special parts 

 in the adult is a secondary result of development. The study of cell- 

 division thus brings us finally to a general consideration of develop- 

 ment which forms the subject of the following chapter. 



LITERATURE. VIII 



Berthold, G. — Studien liber Protoplasma-mechanik. Leipzig^ 1886. 



Boll, Fr. — Das Princip des Wachsthums. Berlin. 1876. 



Bourne, G. C. — A Criticism of tlie Cell-theory ; being an answer to Mr. Sedgwick's 



article on the Inadequacy of the Cellular Theory of Development : Quart. /ourn. 



Mic. Sci., XXXVIII. i. 1895. 



1 Driesch suggests for such a process the term reparation in contradistinction to true 

 regeneration. 



2 '99, p. 55. It is mainly on these consiilerations that Driesch ('99) has built his recent 

 theory of vitalism (r/: p. 417), the nature of the formative power being regarded as a 

 problem sui generis, and one which the " machine-theory of life " is powerless to solve. Cf. 

 also the views of Whitman, p. 416. 



