50 FRANKLIN P. REAGAN 



Hahn calls attention to the fact that if such argument as that 

 of Graper concerning embryo 'A' were valid it could likewise 

 apply to the conditions in Griiper's embryo 'C,' which is above 

 described. I beUeve with Hahn that the question of necessity 

 is inapplicable equally in both cases. In both these instances 

 the development of endothelium was 'unmoglich' whether it 

 was 'unnotig' or not. Griiper's explanation of his embryo 'A' 

 would defeat his own theory of multiple hearts, in that only one 

 is 'notig;' it is inconceivable that all supernumerary heart- 

 anlagen have equal advantages for their own preservation and 

 development. Doubtless in both Graper's embryos 'A' and 'C' 

 he has simply produced conditions such that one-half the heart 

 anlage was unable to develop — otherwise both would have 

 developed bilateral hearts if the embryos were normal prior to 

 operation. If an endocardial anlage ever started on the oper- 

 ated side in either case, it could in all probability have been 

 detected in these embryos when they were sectioned. 



Graper misinterprets Hahn's conclusions when he states that 

 the development of endothehum in his own embryo 'C' dis- 

 proves the vahdity of Hahn's work. So far as I am aware, Hahn 

 did not claim that a destruction of the posterior portion of the 

 primitive streak would inhibit the formation of endothehum. 



Graper's operations were generally performed on such early 

 stages that the orientation of the embryo was uncertain. In 

 some cases his 'posterior' cauterizations were no doubt some- 

 what lateral. 



I am convinced from my ow^n experiments at least, that 

 Graper's one 'fortunate case,' embryo 'C,' is insufficient to over- 

 throw the view of Riickert and Hahn. 



2. The work of Hahn, and Miller and McWhorter 



As we have already seen, the work of Hahn was announced 

 by Riickert in Hertwig's Handbuch before Graper's account 

 was published, but the latter account was published prior to the 

 publication of Hahn's own observations; owing to these cii'cum- 

 stances the work of each was known to the other. Their results 



