518 S. R. DETWILER 
B. Transplantation experiments 
In the transplantation of the hmb mesoderm the method of 
staining with Nile blue sulphate was also employed in a number 
of cases. Of two embryos which were selected, one was stained 
in an aqueous solution of the dye until the desired color had 
been attained. In the other embryo a circular wound was pre- 
pared, posterior to the region of the limb mesoderm, for the 
reception of the transplant. The limb mesoderm with the over- 
lying ectoderm was then excised from the stained embryo (posi- 
tion indicated in text fig. 2) and transferred to the prepared 
7™IN wo UMY 3 
7 7 
-PN 
Fic. 4 Camera drawing of an embryo in the stage of high medullary folds. 
The heavily stippled dise indicates the size and position of the limb mesoderm 
with the overlying ectoderm transplanted from an embryo previously stained 
in a solution of Nile blue sulphate. X 10. 
Fig. 5 Camera drawing of the same embryo shown in figure 4 two days later, 
showing the relation of the transplanted area to the normal limb region. X 10. 
wound (text fig. 4). It is seen from this figure that a transplant 
-so placed occupies the flank region at the very posterior end of 
the embryo. When the embryo had developed so that the 
somites became visible, the position of the stained transplant 
with respect to the somites, as well as its relation to the normal 
limb region, could be ascertained (text fig. 5). Transplants which 
are placed at the position indicated in text figure 4 practically 
always come to lie ventral to the sixth, seventh, and eighth so- 
mites (text fig. 5), a position which is so near the normal limb 
region that conflicts frequently arise in the development of the 
two systems. ‘The limbs which usually start separate. develop- 
ment very often fuse together. In several cases only one limb 
developed from the two systems. In order to obviate these 
