Chromatin as ''Hereditary Substance'' 349 



seems to have been sonictliijio- tallsniaiiic in the word, It liav- 

 ing inspired workers with tlif l)clirf tliat since (K'h-nniners 

 belong to the realm of causality, (jiicst after tluin al).solves 

 the seeker from the huml)Ic task of telling in ordinary de- 

 scriptive fashion what they themselves are. Although no 

 serious effort has been made in tins ])eri()d to give an ac- 

 count, either morphological or [)hysi()logical, of determiners, 

 excepting that they determine, the fact that evidence lias 

 been forthcoming in abundance that cliromosomes act as 

 though they were depositories, or carriers of determiners if 

 such exist, has increasingly vivified and strengthened faith 

 in them, and so has made the determiner hypotliesis a stinm- 

 lant to research in even greater measure than did its im- 

 mediate predecessor, the deternn'nant hypothesis of Wels- 

 mann. 



If the value of a "working hypothesis" is to be .judgt-d 

 solely by the amount of work incited by It (though for rea- 

 sons which it is beyond the scope of this volume to ])resent 

 I deny the adequacy of such valuation), this hypothesis has 

 surely justified itself. If one mentions only the foremost 

 workers in this field the list is by no means short and con- 

 tains biologists of the first rank. The names of Boveri, 

 Correns, Doncaster, Goldschmldt, Guyer, R. Hertwig, King, 

 McClung, Meves, Montgomery, INIorgan, Stevens, and \\. \\. 

 Wilson, would be sure to a])pear in any list of students dis- 

 tinguished for what they have contributed to the advance- 

 ment of biology during the last two decades, and the ]irol)- 

 lem of the cytological basis of heredity has received a gen- 

 erous share of the attention of all these. 



The fruitage of effort since McClung published his hy|)<)- 

 thesis must now be summed up, though naturally only the 

 baldest essentials can be included. McClung conceived the 

 accessory chromosome to be the bearer of those qualities 

 which pertain to the male. In other words, he conceived 

 that maleness in the insects to whicli his studies related was 



