312 NATURAL SCIENCE [November 



its original qualities ; even where the transmission is alternate, we 

 may admit that the different conditions at the different stages of a 

 genetic cycle modify the organisms produced. In the simplest case 

 of collateral transmission, as presented by Volvox globator, the steril- 

 ised colonial cells so closely resemble more primitive independent 

 forms in their behaviour and character, that we may well believe 

 that they have inherited these from such forms, directly and un- 

 altered, from some Protist ancestor, while the reproductive cells have 

 become modified. But it is impossible to suggest such an explana- 

 tion for the higher Animals and Plants, since a nerve-cell with its 

 outgrowths many feet long, or a woody fibre which has expended all 

 its living protoplasm in the building up of a firm wall, can only have 

 been evolved as portions of a highly-specialised colonial organism. 



The difficulty of explaining the mechanism of collateral trans- 

 mission in Metazoa and Metaphytes by the direct transmission in 

 Protista has been the origin of the recent lively discussions on 

 heredity. To biologists saturated with the implicit conviction that 

 only direct cellular transmission was alone possible, some mysterious 

 agency, that should be contained in the reproductive cells, and be 

 handed down by them in their direct cellular descent, was an 

 essential assumption ; and this agency is supplied by Weismann in 

 his Germ-Plasm Theory. The reader will do well to bear in mind 

 that it has been presented to the world in successive editions ; each 

 has been greeted as final by the disciples, who have made light of 

 the objections raised thereto, though on every occasion such objec- 

 tions induced the Master to recast the theory in his next work. 

 Our presentment of the theory upheld in the " Germ Plasm ; A 

 Theory of Heredity," published in London in 1893, may therefore, 

 for aught anyone can tell, become obsolete very shortly, owing to 

 the author's " having (to use his own phrase) in the meantime gained 

 a deeper insight." 



Weismann conceives that in the nucleus of what we have 

 termed ' reproductive ' (and also, in part, ' embryonic ') cells is a 

 mixed plasm, the ' germ-plasm,' composed of certain entities, the 

 ' determinants ' for the several organs of the colony ; that when the 

 cell divides at the limit of growth into two similar cells, the germ- 

 plasm and the several determinants divide in the same way, so that 

 the determinants are the same in each of the daughter-cells as they 

 were in the parent. But in those divisions which give rise to 

 specialised cells the germ-plasm divides as a whole, in such a way 

 that the determinants are only distributed between the daughter- 

 cells, some to one, some to another : we may say that there is 

 distribution or repartition, not the true division of the several 

 determinants. Similarly, the determinants each contain a group of 

 minor entities the biophors, and in the ultimate divisions of the cells 



