244 Ross Granville Harrison 



fact my experiments did actually show^^ that the main chain of 

 organs would grow into the path of the dorsal branch when the 

 former was shifted from its normal course, just as we may suppose 

 the nerves of the lumbo-sacral region to grow under the guidance 

 of the paths in the forelimb. Thus the analogy favors the possi- 

 bility of outgrowth into strange paths and not the opposite asBraus 

 supposes. 



We now come to the second main point made by Braus, which 

 is that an"aneurogenic" extremity when transplanted to a normal 

 individual does not acquire a nervous system. Were the nerves 

 formed as outgrowths from the nerves of the host, Braus argues 

 that they should grow just as readily into "aneurogenic" extrem- 

 ities as into the normal ones.^^ Their failure to do so he regards as 

 sufficient ground for rejecting the outgrowth theory. ^^ It is true 

 one may interpret this result in accordance with Hensen's theory, 

 though in so doing it must be admitted that the differentiation 

 of the nerve fibers is dependent upon the integrity ot their connec- 

 tion with the centers, for the only reason to be given that the 

 nerves have not been formed in the aneurogenic buds at the time 

 of transplantation is because their connection with the centers have 

 been destroyed; not having been in connection during the critical 

 period, their development at any future period is precluded and 

 such limbs remain therefore without nerves. But it is not necessary 

 to refer differences between the "aneurogenic" and the "euneuro- 

 genic" extremities to invisible pre-nervous structures tor, as already 

 mentioned, there are actual visible nerve fibers present in the nor- 

 mal or " euneurogenic " buds at the time of transplantation, while, 

 of course, in the "aneurogenic" ones there are none." But even 

 this tangible difference between the two sorts of limb buds does 

 not actually cause the nerves to behave differently toward them, 

 unless, possibly, the absence of the nerve twigs in the one case 

 retards to a slight extent the development of the nerves, for, as my 



"Op. cit., p. 127. 



i^Braus '05, p. 450. 



i^Braus '05, p. 452. 



"This was given as a possible explanation in my brief criticism of Braus' work (Harrison '06). 

 At that time I did not have the data afforded by my own experiments, which show that as a matter of 

 fact no explanation is necessary. 



