THE METAMORPHOSIS OF LARVA 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 
tailend. 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 larvee, 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 effect 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 
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