INHERITANCE OF ACQUIRED CHARACTERS. ^-J }^ 



Anyway, the consensus of opinion is strongly against Weis- 

 mann's assumption that the chromosomes of different tissues of 

 any particular animal differ from each other. It seems to be 

 more or less proved that the chromatin in any animal does not 

 vary; and if this view is correct, then we must assume that an 

 ovum differs from other cells, in that its cytoplasmic constituents 

 are different. 



But if the specitic nature of the ovum is to be found in 

 the non-chromatic part of the ovtim, then either the ovum must 

 contain some other substance, continuous in the same way as 

 the chromatin, in virtue of which the specific substance is formed 

 in the ovum ; or the specific substance must be formed in the 

 ovum as a result of its position in the whole body. That is, the 

 continuity of the chromatin is not a sufficient phenomenon, since 

 we must necessarily assume a second substance which may be 

 continuous or formed anew in each generation. 



That the second necessary substance is of vital importance 

 is indicated in the case of ova with little or no regulatory power 

 — e.g., in the eggs of ctenophores in which slicing of any por- 

 tions of the ovum results in the absence in the adult of the por- 

 tions sliced. 



And if at least two substances are necessary for develop- 

 ment, of one of which it is impossible to say whether it is con- 

 tinuous or not, how can one say that the hereditary substance is 

 continuous ? 



From the al30ve it will be seen that the case in favour of 

 germinal continuity is not particularly strongly supported by 

 facts. It is, however, still further weakened b}'' definite ex- 

 perimental evidence. For example, the slicing experiments on 

 ctenophorean ova indicate that the " factors " for the adult char- 

 acters are present in the cytoplasm and not in the nucleus. 

 Further, the experiments of Nageli on alpine plants brought to 

 Munich, Schmankewitsch's experiments on brine-shrimps, the 

 experiments of Standfuss and of Fischer on pupa; of butter- 

 flies, and 'Birown-Secjuard's experiments on guinea-])igs. all show 

 that the germ-plasm is not a C(^ntinuous substance, isolated in 

 the soma. Experiments of this kind are usually dismissed with 

 laboured explanations in terms of Weismann's theory ; but any- 

 one who is prepared to dismiss from his mind any ideas as to 

 the theoretical impossibility of acquired characters being here- 

 ditary must acknowledge that the experiments are convincing. 

 The scope of this paper is not such as to allow a discussion of 

 all the cases mentioned, but a few words on one of them, 

 viz., those on butterfly pupae, may be allowed. The germinal 

 discs and gonads in such cases are already present before pupa- 

 tion. If, now the application of heat or cold to the pupa should 

 change the characters of the imago, then, the changes not l:)eing 

 of the nature of secondary sexual characters, these changes must 

 be acquired characters — l.e-, characters acquired by the soma 

 under direct stimulation of the environment. And if, as actually 

 happened, these changes reappeared in some of the next genera- 



