ZOOLOGY: R. a HARRISON 
541 
Experiments. 1. The results of the simple removal of the body wall 
of the limb region are given in the left half of the Table. While the 
figures in the single classes are often not large enough to give significant 
percentages, it is clear that the cleaning of the wound of all scattered 
mesoderm cells reduces very materially the proportion of cases in which 
regeneration occurs, i.e., from 79 to 45 per cent. It is also apparent that 
when the size of the wound exceeds in diameter the length of three 
somites the proportion of cases in which limbs develop is considerably 
less, whether the wound is cleaned or not. When it is carefully cleaned 
and exceeds three somites in diameter, the healing is slow and there 
is a very high mortahty, which accounts for the small number of experi- 
ments with wounds of this size appearing in the tabulation. 
The age of the embryos, within the limits of the stages experimented 
upon, has no influence upon the regenerative capacity. The presence 
of the pronephros, which on account of its close proximity might possibly 
FIG. 1. FIG. 2. 
FIG. 1. EMBRYO OF AMBLYSTOMA PUNCTATUM SHOWING THE WOUND IMMEDIATELY 
AFTER OPERATION IN A TYPICAL EXPERIMENT. X 10. 
FIG. 2. AMBLYSTOMA LARVA FROM WHICH THE LEFT FORE LIMB RUDIMENT WAS 
REMOVED, PRESERVED 87 DAYS AFTER OPERATION. X 5. 
be thought to have some influence on the limb, seems not to affect its 
normal development, for a perfectly normal limb may be formed when 
the pronephros is removed. The removal of this organ facihtates, how- 
ever, the cleaning away of the mesoderm cells and thus may affect indi- 
rectly the results of experiments, even though it exerts no formative 
stimulus. 
The limbs which develop after removal of the rudiment are retarded 
in development to a varying degree. In no case has a hmb been found 
subsequently to arise, when the negative condition has persisted till 
the twelfth day, and in only three cases when it has remained till the 
tenth. Consequently, if development has not begun by the end of the 
second week it is safe to assume that it will not take place at all. A 
large number of cases observed till the end of the third or the fourth 
week, and in some instances much longer, show this to be true (fig. 2). 
