A SUGGESTED MECHANISM FOR THE INHERITANCE 

 OF ACQUIRED CHARACTERS. 



By Thomas F. Dreyer^ B.A., Ph.D. 



A great deal of courage is required to express open doubt 

 as to the truth of Weismann's theory of germinal continuity — 

 a theory which is upheld by the majority of present-day zoolog- 

 ists. Respect for its originator and admiration of his devotion 

 to his work to some extent restrains criticism by a younger 

 generation, but doubts as to the correctness of the theory have 

 been and are frequently expressed. 



The acceptance of Weismann's theory is one of the greatest 

 stumbling-blocks to the Lamarckian, and it is essential that every- 

 one who is interested in the subject should constantly bear in 

 mind in how far it is supported by observed fact. 



Such support is difficult to find, and far from ciunincing: — • 



1. The fact that any particular individual tends to resemble 

 its parents is most simply explained by assuming a genninal con- 

 tinuity; the apparently sim]:)lest explanation is, however, not 

 necessarily more correct than any other. The one most likely 

 to be true will be not the simplest, but the one Avhich is most 

 strongly supported by other observed facts. 



2. The germ cells are, in a few cases, segregated from the 

 somatic cells at a very early stage of segmentation of the ovum. 

 On the other hand, in manv groups- — c.c]., in the Vertebrata — 

 the germ cells are segregated at a very late stage of develop- 

 ment. Further, the cells from which other tissues are derived 

 may also be segregated from the rest of the segmenting ovum 

 at a very early stage; but will anyone on that account speak of 

 the continuity of such tissues? 



3. It has been more or less proved that the chromosomes are 

 continuous for successive o-enerations, and the analogv- between 

 the divisions of the maturing germ-cell chromosomes and the 

 distribution of mendelian factors seem to indicate that the 

 chromosomes are the hereditary substances. Also the fact that 

 the hereditary influences of the father and mother are equal 

 •points to the chromosomes as the carriers of these influences, 

 since it is supposed that they are the only substances received 

 by the progeny in equal proportions from the two parents. That 

 the chromatin is a possible candidate for such a role cannot be 

 denied, but it is not the only candidate. In cell-division the 

 linin is also apparently exactly divided, and in the genesis of the 

 germ cells it is quite possible that equal amounts of linin are con- 

 tained in the large ovum with its difl^use linin and the small 

 spermatozoon with its condensed linin in the form of a " head- 

 piece," metachondria, etc. . 



