NUCLEUS AND CYTOPLASM AS VEHICLES OF 

 HEREDITY^ 



L. C. DUNN 

 BussEY Institution 



There have been of late several attempts to et¥ect a 

 compromise between theories of heredity through the 

 cytoplasm and theories which regard the chromosomes 

 as the vehicles of inherited characters. Conklin ('08) 

 was the first to suggest that egg, embryonic and general 

 phyletic characters of any stage of the organism were 

 determined in the egg cytoplasm while the determiners 

 in the chromosomes made their presence known only 

 through the specific or individual adult characters. Shull 

 (1916) has elaborated this suggestion, and has brought to 

 its support not only the older data on maternal inheritance, 

 matrocline hybrids and the facts of development which 

 relate to polarity, s>Tnmetry and organ-forming sub- 

 stances, but has added new evidence of his own from ex- 

 periments with rotifers. Most recently, Loeb, in his book 

 "The Organism as a Whole," has advanced a similar com- 

 promise theory, based on similar evidence. 



Before examining in detail the experimental basis for 

 such a compromise, it is important that the terms to be 

 used be clearly and unmistakably defined. The first of 

 these is the word "determined." That a character is de- 

 termined in the germ cell means that the differential, 

 causal antecedents of that character are present in the 

 germ cell. It does not mean that the character itself is 

 present in the germ in any form, but rather that it is 

 represented by substances or forces which not only stand 

 for the character but in some way bring about its expres- 

 sion. 



acknowledgement is due. 



286 



