SHOULDER GIRDLE AND ANTERIOR LIMB Saas 
only those components develop which are represented in unre- 
moved tissue. Simple limb-bud extirpations (Exp. A 4, p. 507) 
demonstrate localization of only the more distal portions of the 
rudiment, since in the absence of the central portion, which is 
removed along with the limb bud, isolated elements (supra- 
scapula and coracoid) of the girdle are formed. However, the 
formation of only the dorsal zone following complete removal of 
the rudiment of the ventral zone (Exp. A 5, p. 508) or just the 
opposite experiment (Exp. A 3, p. 506) offers proof that the cen- 
tral portion of the rudiment is also localized and that the ex- 
tirpation of any given portion does not incite restitution proc- 
esses in the unremoved parts. 
The system at this stage may be regarded as a mosaic of which 
the various parts may develop into later known components 
without influence of neighboring portions. Braus (’09, p. 268) 
also called the shoulder-girdle system of Bombinator a mosaic, 
* but only in its normal situation. According to him, when a 
portion of its rudiment is transplanted to a new environment, 
the mosaic is lost and the implanted tissue acquires the capacity 
of reversing differentiation which had already appeared in the 
anlage, so that it is now able to form anew an entire girdle. 
Accordingly, transplantation incites restitution, and the system, 
which in its normal environment is a mosaic, in the new environ- 
ment becomes an equipotential one. 
Although Braus found that the shoulder girdles which de- 
veloped from implantations of only a portion of the rudiment 
were of reduced size (one-third to two-thirds the size of the 
normal), nevertheless, they were regarded by him as entire, 
just as complete individuals of reduced size are formed from 
isolated blastomeres in the cleavage stage of an egg or from 
fertilized egg fragments. While the girdles which had developed 
at the implanted place were formed in all cases from the central 
portion of the rudiment, since it is this portion which is included 
with the limb cells, Braus nevertheless questioned whether there 
was any greater inherent capacity on the part of any portion of 
the anlage over any other in the process of restitution. Ac- 
cording to this idea, the entire structure might develop from 
