THE STRUCTURE OF PROTOPLASM. 19 



What light, if any, do the foregoing general conclusions 

 throw on the theoretical views outlined at the beginning of this 

 lecture ? The answer must be : None that is clear and satis- 

 factory, for the background of all the phenomena appears to 

 lie in the invisible organization of a substance which seems to 

 the eye homogeneous. Yet there is, I think, much in these 

 conclusions to suggest, and nothing to contradict, the hypothesis 

 that the " homogeneous " or "continuous" substance may be 

 composed of ultra-microscopical bodies by the growth and dif- 

 ferentiation of which the visible elements arise, and which differ 

 among themselves chemically and otherwise, as is the case with 

 the larger masses to which they give rise. I will not enter 

 upon a discussion of the question whether these bodies are 

 merely molecules, more or less complex, or groups of molecules 

 forming protoplasmic units or micellae, but will only make three 

 suggestions. First, if such units exist, they cannot be identi- 

 fied with the visible granules or " bioblasts " of Altmann, but 

 are bodies far smaller. Second, if there be any truth in what 

 has been said above regarding the localization of " living " 

 matter in the cell, such protoplasmic units, if they exist, cannot 

 properly be called " biophores," since life is a manifestation of 

 the system which they form and not of the individual units. 

 The corpuscular or micellar theory of protoplasm, as an hypoth- 

 esis of morphological organization, should not be confounded 

 with the physiological theory that biophores or pangens are 

 " elementary living units." Third, by ascribing to these hypo- 

 thetical units the power of growth and division, in accordance 

 with the pangen theory, we are enabled to get a certain amount 

 of light upon some of the most puzzling questions of cytology, 

 such, for example, as the ultimate nature and origin of dividing 

 cell-organs like the nucleus or the plastids, and especially such 

 a contradiction as that presented by the centrosome which may 

 apparently arise either de novo or by division of a preexisting 

 body of the same kind. As De Vries and Wiesner have so 

 suggestively urged, the power of division on which the law of 

 genetic continuity rests and which is manifested by morphologi- 

 cal aggregates of so many different degrees, may have its root 

 in a like power of the primary units at the bottom of the series, 



