240 Ross Granville Harrison 



based upon a new series of experiments similar to those of Braus 

 and Banchi. Before describing the new experiments it will be 

 necessary to consider the previous work in detail, beginning with 

 that of Braus, the main facts of which are as follows: 



1 If an extremity is taken at a time when it is beginning to develop and is trans- 

 planted to any region of aHother tadpole, it will continue its development in the 

 new position and ultimately be found to contain all of the parts — muscles, skeleton, 

 blood vessels and nerves — which are perfectly normal both as to structure and 

 arrangement. The nerves are connected with the nerves supplying the region of 

 the host into which the limb has been implanted, as, for instance, with the facial 

 nerve when the limb is placed on the side of the head in the region of the orbito- 

 hyoid muscle, or with the nerves of the lumbo-sacral plexus when a fore limb is 

 transplanted to the hind limb region. But the nerves within these transplanted 

 extremities, in spite of their unusual origin, ramify exactly as the nerves in a limb 

 in its natural position. Furthermore, these nerves are functional, both voluntary 

 movements of the limbs and movements in response to electrical stimulation having 

 been observed. In considering this experiment, Braus lays great stress upon the 

 point that at the time of transplantation either there are no visibly differentiated 

 nerves within the limb,^ or, if nerves are present, they degenerate and disappear very 

 soon after; the latter was the case in his earlier experiments. 



2 In a second series of experiments limb buds were taken from larvae, from 

 which the whole spinal cord had been removed at a period just after the closure 

 of the medullary folds. Such embryos develop normally aside from the defect 

 caused by the wound, but they contain no nerves except those arising in the head.* 

 Extremities taken from individuals of this character Braus terms "aneurogenic," 

 in contradistinction to the normal ones which are called "euneurogenic." The 

 aneurogenic buds were taken from the nerveless larvae ten days after the removal 

 of the spinal cord and implanted into the hind limb region of normal individuals. 

 Eight days later these larvae were preserved but, although the transplanted limbs 

 had developed considerably, no nerves were found in them, whereas a normal or 

 euneurogenic transplanted bud would have contained nerves by this time. 



3 The normal transplanted limbs acquire, as stated above, nerves which take 

 a normal course. Examination of such limbs in a state of incomplete develop- 

 ment, for example, about three weeks after transplantation, shows that the nerve 

 trunks within them are much thicker than the nerves of the host with which they 

 are connected. 



^Braus '05, p. 438. 

 ■•Harrison '04. 



