THE METAMORPHOSIS or LABV.E 437 



Amblystoma is well adapted to an experiment of this kind. 

 The larva loses an organ at each end in the process of 

 metamorphosis the three large external gills at the head 

 end of the animal, as well as the so-called tail fin at the 

 tail end. Both disappear simultaneously in normal animals 

 in a few days; at the same time an alteration occurs in the 

 pigmentation and marking of the skin. One could not state 

 a priori how a division of the spinal cord would influence 

 the processes of development, for it is well known that 

 immediately after the division of the spinal cord in dogs 

 severe changes usually occur in the condition of the skin of 

 the posterior portions of the body, which may lead to the 

 formation of abscesses, which later again disappear (Goltz). 



Division of the spinal cord (close behind the cervical 

 region) did not have even the slightest effect in a single 

 instance upon the processes of development; metamorphosis 

 occurred just as though the animal were uninjured. This 

 was the more remarkable as in some cases a metamorphosis 

 occurred immediately after the division of the spinal cord, 

 while the wound was still open. I believed at first, on the 

 basis of these experiments, that division of the spinal cord 

 might accelerate the metamorphosis of the larvse, or cause it 

 directly. I found, however, that this was not the case. One 

 animal, for example, was still in the larval stage six weeks 

 after the operation, while the uninjured control animals had 

 already completed metamorphosis. 



Since the experiments showed without exception that 

 division of the spinal cord had no eifect upon the meta- 

 morphic processes, we must state in detail what evidence we 

 have to show that the cord was indeed severed entirely. 

 First of all the operation was made in such a way that the 

 separation of the two ends of the spinal cord could be seen 

 directly in the bottom of the wound. Secondly, the pos- 

 terior part of the body was paralyzed, that is to say, it was 



