508 Ss. R. DETWILER 
TABLE 4 
Showing the effects on the girdle of removal of the limb dise 
CONDITION OF THE GIRDLE 
INDIVIDUAL AGE | 
Suprascapula Seapula Procoracoid Coracoid Shoulder joint 
days 
1 WPA 5 20 present absent |present present absent * 
Ho 20 present* absent |fragmentary| present absent 
* Dorsal half only. 
girdle following a typical limb-bud extirpation not only indicates 
that part of its rudiment is removed with the limb bud, but that 
the part which is unremoved is already determined at the time 
of the operation. Further, when a limb bud is transplanted to a 
heterotopic position, the development of a girdle with a ventral 
zone of reduced size (fig. 28) also serves to indicate that only a 
portion of the rudiment is transferred with the limb cells. 
If localization of the cells which are to form the ventral zone 
of the girdle is complete at the time of the operation and they 
can be successfully extirpated, then only the dorsal zone should 
develop following their excision. <A series of experiments were 
therefore performed to test the validity of this hypothesis. 
5. Removal of the rudiment of the ventral zone of the girdle. It 
is obvious, in the light of experiments previously described (A 3 
and A 4), that, in attempts to extirpate the entire rudiment of 
the ventral zone, the excision must include not only a portion 
of the limb bud, but tissue lying still more ventral than this 
area. In these experiments the mesoderm within the area a-e X 
4-8 was excised and the wounds cleaned and covered. While 
in seventy-five per cent of the cases normal limbs developed 
following excision of this area, it was found that, in a number of 
larvae sectioned twenty days after the operation, the ventral 
zone of the girdle was entirely wanting while the dorsal zone had 
developed normally (figs. 11, 12, and 29 and table 5). Several 
cases similar to the one figured, in which the entire rudiment of 
the ventral zone had been removed, not only lacked the pro- — 
coracoid and coracoid elements, but the shoulder joint as well. 
