524 Ss. R. DETWILER 
either the dorsal or ventral parts of the rudiments, yet no ex- 
periments were made to test the validity of this hypothesis. 
While Braus (09, p. 27) claimed that this system in Bombina- 
tor is equipotential from stage 2, when the limb bud is very small, 
up to the time of chondrification of the humerus, it is clear from 
experiments described in this paper that such is not the case in 
Amblystoma. 
It has been shown, that when only the ventral portion of the 
rudiment was transplanted with the limb cells, only the corre- 
sponding zone of the girdle developed (figs. 15 and 32), just as 
when the dorsal half of the rudiment was transplanted with the 
limb cells, it developed into a girdle which was composed almost 
entirely of a dorsal zone (figs. 16 and 33). The presence of a 
very small portion of the ventral zone in these cases is no doubt 
due to the inclusion in the transplant of some of the cells which 
are to form the ventral zone, since it is difficult to separate accu- 
rately the two halves of the rudiment. The failure, however, of 
these cells to form a complete ventral zone shows their lack of 
the potency to form this portion of the girdle. 
Although the girdle rudiment of Amblystoma, when trans- 
planted, may not be regarded as a perfect mosaic, since slightly 
more cartilage may form from portions of the rudiment than 
would have formed had they not been transplanted, yet it is 
obvious that it cannot be regarded as an equipotential system 
at the stage with which we are dealing. In a true equipotential 
system such as the limb rudiment, the extirpation of any portion 
does not lead to any definite defects in the components of the 
limb which develop from the unremoved portion of the rudi- 
ment. Even after extirpation of a half of the rudiment, normal 
limbs with all their cartilaginous and muscular elements may 
develop. The same thing is true when a half of the limb rudi- 
ment is transplanted. In this case two limbs of normal size 
and structure may develop, one from the transplant and the 
other from the unremoved half of the rudiment. 
Definite defects in the girdle resulting from removal of certain 
portions of its rudiment, as well as the formation of girdles with 
only dorsal or ventral halves resulting from the transplantation 
