SUPPOSED TRANSMISSION OF ACQUIRED CHARACTERS 395 



according to the primary constituents which they contain ; and 

 this is done as equally as possible, or, at any rate, in a definitely 

 prescribed manner. Why should the centrosomes and spindle- 

 threads be present, and the longitudinal fission of the idants 

 occur, if myriads of primary constituents of the germ-plasm 

 circulate separately through the body, and are capable of enter- 

 ins: the serm- and other cells from without, as well as of 

 becoming properly arranged in them in the order in which they 

 subsequently undergo development? Why should nature be 

 so scrupulously careful to divide the idants as accurately as 

 possible, if their composition were open to alteration at any 

 moment by the entrance of new primary constituents or gem- 

 mules ? T/ie process of the fission of the idioplasm in nuclear 

 and cell-division seems to me directly and cotichisively to refute 

 the •whole idea of the circulation of gem mules. For the \ery 

 reason that these nuclear rods or idants can never receive an 

 addition of new primary constituents from without, the most 

 extreme care is required, during their multiplication by division, 

 to prevent the different qualities of the mother-cell from being 

 distributed improperly amongst the daughter-cells, and causing 

 an irreparable loss of certain primary constituents to one of the 

 latter and its descendants. 



It is impossible to assume the transmission of somatogenic 

 variations in any theory which accepts the nuclear substance 

 of the germ-cells as germ-plasm or ' hereditary substance ' ; for 

 it is theoretically impossible to account for these variations, no 

 matter how ingeniouslv the theory is constructed. 



At the present day I can therefore state my conviction still 

 more decidedly than formerly, that all permanent — i.e., heredi- 

 tary — variations of the body proceed from primary modifications 

 of the primary constituents of the germ ; and that neither injuries, 

 functional hypertrophy and atrophy, structural variations due to 

 the effect of temperature or nutrition, nor any other influence of 

 environment on the body, can be communicated to the germ- 

 cells, and so become transmissible. 



This statement naturally implies the rejection of Lamarck's 

 principle of variation ; for those factors which this talented 

 philosopher and investigator believed to be all-important in the 

 modification of species, — viz., the u.se and disuse of parts, — can 

 have had no direct share in the process. I am by no means the 

 only one to hold this view at the present day ; and although 



