542 
ZOOLOGY: R. G. HARRISON 
No extensive examination of the material has been made by means 
of sections, but five cases which were cut show, that even though the 
free appendage is lacking, a shoulder girdle of somewhat reduced dimen- 
sions is developed on the operated side, just as Braus^ has found in the 
case of Bomhinator. 
2. The experiments of the second group, in which limited portions of 
the limb rudiment were removed — dorsal, ventral, caudal, or rostral 
half, or the central portion — all resulted in the formation of perfect 
limbs whose development was but slightly retarded. 
3. A comparison of the right and left halves of the Table shows at a 
glance that the covering of the wound with indifferent skin is a con- 
siderable hindrance to the development of the limb. The cases, cited 
on the first line of the table, in which the wounds were not cleaned 
happen to give, however, a considerably exaggerated idea of the effect 
of skin transplantation, since the control experiments in which the 
wound was left uncovered, made at the same time and with the same 
material, showed also a very high percentage of cases of non-develop- 
ment. Some unknown factor must have affected the results here. The 
cases in which the wound was cleaned are gathered, however, from experi- 
ments made at various times, and these show very clearly the effect of 
covering the wound. In the experiments with wounds of but three 
somites in diameter the percentage of development is reduced from 52 
to 33, while in the cases where the wound is three and a half segments 
or more in diameter, i.e., when the region of the anterior half of the 
sixth segment is included, the percentage of development is reduced to 
zero. The determination of this latter point is of prime importance 
for the main purpose of this work, since it shows how much it is neces- 
sary to remove, when transplanting other buds to the limb region, in 
order to be sure that the appendage which develops is not simply regen- 
erated from the host. 
4. The experiments in which the ectoderm of the limb region was 
healed back in place after removal of the mesoderm are only ten in 
number and are, therefore, insufficient to give significant percentages. 
They nevertheless confirm the result of the previous series. Five experi- 
ments with wounds of three segments in diameter yielded three cases 
in which development occurred and two in which it did not occur. 
Five other experiments with wounds four segments in diameter were all 
negative. The mesoderm was carefully cleaned off at the time of the 
operation in all experiments of this set. 
5. The five cases in which the ectoderm alone was removed and the 
mesoderm, at least in great part, left in place all resulted in the develop- 
