532 



THE AMERICAN NATURALIST [Vol. LT 



Sex, the inheritance of which is shown in many cases to 



be associated with sex chromosomes ; 

 ''Apterous," loss of wings in certain stocks of Droso- 



Eyeless," partial or complete loss of eyes; 

 ''Extra legs," duplication of part or of entire legs which 



in one race shows Mendelian sex-linked transmission; 

 Heliotropism, loss of positive resi>onse to light in one 



stock of Drosophila, 



Until there is forthcoming some direct evidence that the 

 cytoplasm apart from its contained plastids transmits 

 .more fundamental characteristics than the chromosomes, 

 the claim that such a difference exists is not only entirely 

 speculative, but has been shown not to be true for a num- 

 ber of characters. No doubt the idea arose from the fact 

 that when the egg begins to develop it is the protoplasm 

 that exhibits most of the phenomena concerned with the 

 early development of the axial and bilateral relations, the 

 type of cleavage and the formation of the organs of the 

 embryo. But this kind of evidence shows no more than 

 that these characteristics are then present in the cyto- 

 plasm ; it does not show whether they have come from the 

 clironiosomcs iii tlie enrlv history of the egg cell, or were, 

 as assiiiiKMl. inlicivnt lu'opcrties of the cytoplasm as such. 

 In recent ii(i\ve\ei', it has been possible in a few 



cases, like tli()>e ol lovaiiia, to i^et exi>erimental evidence 

 l)eaiirig on this point and it lias sliowii bcvond dispute 

 that such cUoplasmic txpe- of Ix Immoi .im itn])iessed on 

 the cytoplasm by the chromatin in the same wav jiresum- 

 ably as are all Mendelian chnraeienstio. 



No one has denied, so rai- as I know, that tiie evtoplasm 

 is essential for de\ eh.piiH nt Tliat it 1 1 iiiMiii t ted 

 largelv, if not entirelv. thi'ouuh the evtonhM-in ol tii<' 



