526 S. R. DETWILER 
larger than that which developed from the same sized area from 
an older embryo. As has already been shown, this is not the 
case in Amblystoma between the stage of open medullary folds 
and the tail-bud stage. These stages, however, are younger 
than any used by Braus. 
Variations, therefore, in the size of the implanted girdle are 
to be regarded as an expression of a greater or less amount of 
girdle rudiment having been included with the transplanted 
limb mesoderm. 
5. SUMMARY 
1. The separate parts of the shoulder-girdle rudiment of 
Amblystoma punctatum are already determined at the stage 
when the limb rudiment is present as a definite thickening of 
the somatopleure (Stage 29). 
2. The removal of a definite portion of the rudiment brings 
about a defect in that portion of the girdle corresponding to the 
part removed. 
3. The extirpation of a given portion of the rudiment does not 
incite restitution processes in the unremoved parts. In the ab- 
sence of the central part of the girdle the gap may be bridged 
over by a hyperplastic development of those elements which are 
formed from the unremoved portions of the rudiment. 
4. The suprascapula develops ‘in situ’ from a separate rudi- 
ment, the extirpation of which has no effect on the development 
of the limb nor on the remainder of the girdle (Exp. A 1, fig. 24, 
and table 1). 
5. Complete extirpation of the third, fourth, and fifth somites, 
while having no effect on the musculature of the limb, does, 
however, produce marked defects on the ventro-lateral muscula- 
ture (Exp. A 2). These results corroborate those of Byrnes 
(98) and Lewis (’10). 
6. The central portion of the girdle rudiment is carried along 
in the transplantation of a typical limb bud (text fig. 1) and a 
girdle of about one-third the size of the normal develops at the 
place of implantation (fig. 21; ef. fig. 22). 
7. It is possible to initiate the development of a limb in 
