540 
ZOOLOGY: R. G. HARRISON 
6. Transplantation of small masses of mesoderm, not yet visibly differ- 
entiated, from the limb region to pockets mider the skin on the side 
of the embryo. 
The fore limb appears at a much earlier stage than the hind limb in 
the Urodeles and much earlier than either extremity in the Anurans. 
The operations were consequently done upon embryos about the time 
Table showing effect of removal of body wall of fore-limb region, the mmber of cases in each 
category being given 
SIZE OF WOUND 
WOUND NOT COVERED 
WOUND COVERED 
Not cleaned 
Cleaned 
Not cleaned 
Cleaned 
Regen. 
Not 
regen. 
Regen. 
Not 
regen. 
Regen. 
Not 
regen. 
Regen. 
Not 
regen. 
Not recorded 
11 
9 
2 
8 
22 
1 
13 
12 
7 
14 
3 
2 
3 J somites 
1 
0 
1 
0 
0 
1 
25 
8 
2 
7 
0 
11 
0 
2 
16 
2 
-2 
3 
0 
3 
0 
2 
4| somites 
2 
0 
Total 
76** 
79 
20 
21 
18 
45 
22 
55 
2 
20 
8 
80 
11 
24 
35 
76 
* In the groups so marked the ectoderm of the limb region was healed back in place; in the other groups in 
which the wound was covered ectoderm from other regions of the body was used. 
** Includes five cases, constituting the fifth group of experiments, in which a large part of the mesoderm was 
purposely left in. 
of appearance of the tail bud (fig. 1). In many cases, however, the 
embryos were slightly younger or slightly older than the one shown 
in the figure. The fore limb of Ambly stoma develops as a thickening 
of the somatopleure which centers in the region of the fourth myotome 
and extends over into that of the third and fifth. In order to remove 
the tissues which form the appendage, a circular incision of about the 
diameter of these three segments was made with fine scissors, and the 
loosened piece including both ectoderm and mesoderm was then torn 
free and removed. The few mesoderm cells which are usually left 
sticking to the pronephros and around the edges of the wound were 
carefully removed in some cases and in others left in place. In some 
individuals the pronephros was left intact and in others it was removed. 
In nearly all cases the operation was done on one side, the other being 
left in its normal condition for comparison. 
