282 Experimental Zoology 



ing here, no doubt, with an extremely elusive and difficult prob- 

 lem, but one that is of fundamental importance in all 

 questions in which the problem of organic form appears. It 

 may be that there are factors at work here of which as yet we 

 have Httle real conception, and any such attempt as this that I 

 have made to give the facts an explanation on more or less famil- 

 iar assumptions may be premature. I hope, nevertheless, that 

 I may have succeeded in calhng attention to certain important 

 phenomena of growth, and even if my attempt to bring the re- 

 sults under one point of view should prove unsatisfactory, the 

 attempt may at least serve as a suggestion for further work 

 along these lines. 



To sum up : I have attempted to account for certain phe- 

 nomena of regeneration by a process of growth in which the 

 following factors appear to enter: (i) the differentiated material 

 as a factor in Hmiting the character of new parts ; (2) the relation 

 of the cells to each other as a factor in their differentiation, and 

 assume that this relation is due to the mutual pressures or 

 tensions of the cells on each other; (3) the differentiated cells 

 also determine the existing tension in that part, and this may 

 in turn react on the new cells with which they are in contact. 

 Remove a part and the pressure relations are upset, but this 

 leads ultimately to the reestablishment again of the same rela- 

 tions of pressure. 



LITERATURE, CHAPTER XVII 



King, H. D. Further Studies on the Regeneration of Asterias vulgaris. 



Arch. f. Entw.-mech, IX. 1900. 

 Morgan, T. H. Regeneration. 1901. 



The Physiology of Regeneration. Jour. Exp. Zool. III. 1906. 

 Spallanzani, L. Prodromo di un' opera sopra le Riproduzioni animali. 



1826. 

 Weismann, a. Essays upon Heredity. Trans. 1891-1892. 

 Zeleny, C. a Study of the Regeneration of the Arms of the Brittle-Star. 



Biol. Bull. VI. 1903. 

 Compensatory Regulation. Jour. Exp. Zool. II. 1905. 



