SHOULDER GIRDLE AND ANTERIOR LIMB 517 
TABLE 7 
Showing the effect of removal of the limb mesoderm from embryos in the stage of 
high medullary folds 
WOUNDS COVERED WOUNDS NOT COVERED 
SIZE OF WOUND, 
DIAMETER | 
Regenerated Not regenerated Regenerated Not regenerated 
mm. 
Not recorded 10 23 7 14 
0.66 6 0 
O.3% 6 2 
0.80 oil 3 
0.86 0 3 
0.93T 0 5 
* Equals the size of a three-somite wound. 
+ Equals the size of a three-and-one-half-somite wound. 
excised areas were taken undoubtedly occur because of the ab- 
sence of definite surface markings, nevertheless, the results of the 
table show that, as the diameter of the excised area approaches 
the diameter of a three-and-one-half somite wound, less regen- 
eration occurs. 
While the limb mesoderm ean be successfully extirpated from 
embryos of this stage certain technical difficulties are met with 
in the procedure. Although healing of the tissue is rapid, the 
embryos frequently disintegrate a day or two after the opera- 
tion. It was found that a smaller number disintegrated if they 
were kept at a temperature of about 15°C. for twenty-four 
hours after the operation and then brought back to room tem-. 
perature. 
Watch glasses which were used in these operations were coated 
either with wax or paraffin in order to prevent the embryos from 
sticking to the bottom. If this is not done, they frequently 
adhere to the glass and the ectoderm is torn off in attempts to 
liberate them. Embryos should remain in these coated dishes 
for from twelve to twenty-four hours after the operation. They - 
ean then be transferred with safety to ordinary watch glasses. 
