522 S. R. DETWILER 
of a double girdle. In all cases studied a single girdle was 
formed. If the two members of a double limb are completely 
fused at the base there is only one shoulder joint; if they are 
separated at the base two joints may be formed on the same 
girdle. 
According to Braus (09, p. 283), when reduplicating limbs arise 
from a single transplanted rudiment of Bombinator, there may 
be a complete reduplication of the implanted girdle; or, in addi- 
tion to the formation of one main girdle for the principal limb, 
there may be an accessory girdle for the supernumerary append- 
age (Braus, op. cit., p. 284, and pl. 16, fig. 5 a). 
It is evident from the cases cited (D 23, 29, 41) in which 
girdles from three-fourths to four-fifths the size of the normal 
had developed, that all or nearly all of the rudiment must have 
been included in the transplant. Their being slightly smaller 
than the normal is probably due to the fact that they are placed 
in an abnormal environment where there is less space for differ- 
entiation than in the normal situation. 
Girdles which develop from typical limb-bud transplantations 
in embryos of the tail-bud stage (text fig. 1) are never as large 
when compared with the normal as those which have just been 
described. When the girdle shown in figure 21, which is a typi- 
eal result of such a transplant, is compared with the normal 
girdle of the same larva (fig. 22), it is found to be only one-third 
as large. ‘The difference in size of the implanted girdles in the 
two cases becomes explicable when it is seen that in one case 
(fig. 21) only the central portion of the girdle rudiment is trans- 
planted with the limb mesoderm, while in the other (fig. 20) all, or 
nearly all, of the rudiment is included. 
4. DISCUSSION 
In the embryos of Amblystoma individual portions of the 
shoulder-girdle rudiment are determined at the stage when the 
limb tissue is present as a definite somatopleural thickening 
(stage 29). Experimental evidence has been advanced to show 
that after extirpation of any definite portions of the rudiment 
