622 



SCIENCE. 



[N. S. Vol. XV. No. 381. 



credit of first having shown the inability of 

 natural selection to explain certain cases of 

 regenerative adaptation belongs to Gustav 

 Wolff rather than to Morgan, but the latter 

 has greatly enlarged and extended the evi- 

 dence in favor of this position. Nevertheless 

 the author is conservative in his treatment 

 of this question ; he launches into no ' railing 

 accusations' against natural selection, but is 

 content to point out its insufficiency in the 

 cases under discussion, wisely leaving others 

 to draw their own conclusions as to its general 

 applicability. 



Likewise in his treatment of the theories 

 of development and regeneration the author 

 shows a wise conservatism which is in refresh- 

 ing contrast to some of the revolutionary as- 

 sertions of the earlier stages of Entwicklungs- 

 mechanik. The author's conclusion that 

 regeneration and development belong to the 

 same general group of phenomena and that 

 the same problems are met with in the two is 

 a most important and valuable one. His pres- 

 ent position that the development of egg frag- 

 ments is only a special case of regeneration 

 plus the phenomena of development is funda- 

 mentally like the view expressed earlier by 

 Eoux ('93) and unlike the position which 

 Driesch and Morgan formerly maintained. 

 Thus he says (p. 24Y) : "We have, however, no 

 reason to suppose that all the (cleavage) cells 

 are alike because they are all potentially equal. 

 Even pieces of an adult animal — of hydra or 

 of stentor, for example — can produce new 

 whole organisms, although we must suppose 

 these pieces to be at first as unlike as are the 

 parts of the body from which they arise. 

 Moreover we do not know of a single egg or 

 embryo in which we cannot readily detect dif- 

 ferences in different parts of the protoplasm." 

 Contrast this with Driesch's famous dictum, 

 ' By segmentation perfectly homogeneous 

 parts are formed capable of any fate,' or with 

 Morgan's former statement that 'the micro- 

 meres (of the sea-urchin egg) are undifferen- 

 tiated blastomeres, and are not set aside to 

 form any special organ, because normal em- 

 brj'os still come from such fragments without 

 micromeres.' 



The author finds the great problems of de- 



velopment and regeneration centering in the 

 determination of the causes of differentiation 

 and these causes he finds in the organization. 

 What this organization is, however, cannot be 

 explained any more than the physicist can 

 explain what gravity is. The author does not 

 conceive this organization to be the outcome of 

 the integration of biophores or other 'vital 

 units,' nor can it be identified with cells. 

 "Just as the properties of sugar are peculiar 

 to the molecule and cannot be accounted for 

 as the sum total of the properties of the atoms 

 of carbon, hydrogen and oxygen of which the 

 molecule is made up, so the properties of the 

 organism are connected with its whole organ- 

 ization and are not simply those of its indi- 

 vidual cells or lower units." The smallest 

 pieces of organisms capable of regeneration 

 are enormously larger than individual cells, 

 and therefore 'the organization is a compara- 

 tively large structure.' It seems to me that in 

 this matter the author loses sight of the fact 

 that organization like individuality is a thing 

 of degrees and stages. There is undoubtedly 

 such a thing as the cell organization and this 

 is capable of performing certain functions; 

 whether or not it is able to perform the func- 

 tion of regeneration depends upon the animal 

 in question. In protozoa and the egg cells 

 of metazoa it is capable of regeneration as 

 well as of all other functions; in adult 

 metazoa regeneration can be accomplished 

 only by pieces larger than cells, i. r., by an 

 organization of a higher order than that of 

 the cell. 



In connection with the question of organ- 

 ization the author makes the pregnant sugges- 

 tion that it may consist in a system of ten- 

 sions in the living substance rather than in 

 the polarity or other properties of ultimate 

 units. Such a view would accord well with 

 the facts of regeneration and while 'we cannot 

 picture to ourselves in a mechanical way just 

 how such a system could bring about the sup- 

 pression of growth in one region and allow the 

 maximum amount in another region,' it not 

 only accords well with the facts but brings a 

 large number of phenomena under a common 

 point of view. 



However attractive neo-vitalism may be for 



