SYMMETRY IN TRANSPLANTED LIMBS 93 
Bateson, in his ''Materials for the Study of Variation" ('94), 
has given an exhaustive review of the literature relating to super- 
numerary parts, in which the limbs are fully considered. In this 
treatise he has made a masterly analysis of the available material, 
particularly with reference to the appendages of arthropods. 
The phase of the problem which is especially relevant to the pres- 
ent discussion is that concerning what Bateson calls minor sym- 
metries, in which the supernumeraries are in some way symmetri- 
cal with respect to themselves or to the normal appendages with 
which they are associated. The other class of supernumeraries, 
in which two identical appendages stand in simple succession to 
one another are, according to Bateson, practically unknown, 
and even those that have been described are considered by him to 
be of somewhat doubtful nature, though many cases of simple 
hyperdactyly would seem to belong in this category. 
The symmetrical extra appendages fall into two groups: 1) 
those in which there is a pair of extra members symmetrical with 
themselves, arising from the normal appendage with which one 
of the supernumeraries appears to have a definite relation of 
symmetry, and, 2) those in which the single supernumerary is 
symmetrical wdth respect to the normal. The former condition 
Bateson considers to be the more usual, and, in fact, he accepts 
the existence of the latter wdth a certain skepticism which seems 
unnecessary, i"! It is true that many cases that apparently fall 
within the latter group may upon closer examination be found to 
belong in the former, but the converse is also true, as will be shown 
below (p. 97). Bateson has devoted special attention to the 
first group, and, on the basis of about one hundred and twentj' 
cases in insects and a considerable number in the Crustacea, he 
has formulated the following rules, ^''^ showing the relation of the 
supernumerary appendages to each other and to the original 
member : 
I. The long axes of the normal appendage and of the two extra 
appendages are in one plane : of the two extra appendages one is there- 
fore nearer to the axis of the normal appendage and the other is remoter 
from it. 
i"! Op. cit. p. 539 and 553. Consider, however, in this connection, the clear 
case described by Bender ('06). 
102 Op. cit. p. 479. 
