504 S. R. DETWILER 
TABLE 1 
Showing the results following the removal of the area a-e X 1-3 (text fig. 1) including 
the outer cell layer of the somites and the pronephros 
2m CONDITION OF THE GIRDLE AND THE EXTREMITY 
INDIVIDUAL} AFTER 
al Supraseapula Scapula Procoracoid Coracoid Humerus 
FSi 26 absent present present present present 
BaslO a) 24 absent* present present present present 
Rea es 26 absent present present present present 
15; (O55 seree 26 absent present present present present 
* Only dorsal half wanting. ‘ 
ventral halves of the somites and the pronephros, results in the 
formation of a girdle without a suprascapula (fig. 24 and table 1). 
The removal of this area has practically no effect on the de- 
velopment of the extremity itself and of the remainder of the 
girdle. Abnormalities in the limb sometimes occur if its rudi- 
ment is disturbed to any great extent during the operation. 
2. Removal of the suprascapula rudiment and of the myotomes. 
This type of experiment consisted in the entire removal of the 
third, fourth, and fifth somites and the pronephros. In these 
experiments the wound was usually covered with ectoderm taken 
from a second embryo, since complete exposure of the notochord 
and the medullary tube frequently results in a disintegration 
of the embryo. Removal of the entire somites produces the same 
effect on the girdle as that described for the first type of experi- 
ment, viz., the formation of a girdle without a suprascapula 
(figs. 8 and 25 and table 2). In the absence of the somites, the 
limb and the girdle undergo a dorsal shifting (fig. 8). This is 
apparently due to a release of pressure from that direction. 
Complete removal of the third, fourth, and fifth somites, 
while leading to no defects in the limb musculature, brings 
about marked deficiencies in the ventro-lateral musculature, ob- 
servations corroborating those previously made by Miss Byrnes 
(98) and Lewis (10). Miss Byrnes (op. cit.) produced the first 
experimental evidence to show that the musculature of the an- 
terior limb of Amblystoma develops in situ and that it is in no 
way derived from the myotomes or their ventral processes. 
