ZOOLOGY: R. a HARRISON 
245 
ologic conditions of the eggs which these investigators used. These 
variations have now been adequately described and measured, and 
correlated with physiologic condition of the eggs. For experimental 
work it is absolutely necessary to determine in advance the exact physi- 
ologic condition of the eggs, and to use only such, as are nearly in the 
same condition. We may then hope to obtain more constant and pre- 
dictable results. 
A full account of these experiments will appear in the forthcoming 
volume of the Researches of the Marine Biological Laboratory of the 
Carnegie Institution of Washington. 
TRANSPLANTATION OF LIMBS 
By Ross G. Harrison 
OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY 
Read before the Academy, November 14, 1916 
The specificity of the tissue of the limb bud in the amphibian em- 
bryo has been clearly shown by Braus,^ who found that when trans- 
planted to any part of the body it would develop into a normal append- 
age. Since then evidence has accumulated^ to show that the limb 
rudiment, and more especially its mesoderm, constitutes an equipoten- 
tial system. 3 Legs are, nevertheless, rights or lefts and, having no 
plane or axis of symmetry, the leg of one side of the body cannot be 
superimposed upon that of the other. In the early embryonic condi- 
tion, however, there is no visible evidence of laterality, and the ques- 
tion arises when and how this property is determined. Experiments 
made during the past year have rendered it possible to state more sim- 
ply than before^ the rules that govern its determination. 
All of the experiments here considered were made with the fore limb 
of Amblystoma punctatum under precautions necessary to prevent 
regeneration from the host.^ In grafting the limb buds three different 
circumstances relating to their position in the embryo were taken into 
account — location, laterality and orientation (fig. 1). First, the limb 
buds were placed either in their natural location in another embryo 
after removal of the normal bud (orthotopic transplantation) or else 
in some other region of the body, preferably on the flank of the em- 
bryo between the normal fore and hind limbs (heterotopic transplanta- 
tion). Secondly, some were grafted on the same side of the body as 
that from which they were taken (homopleural) and others on the op- 
posite side (heteropleural) . Thirdly, they were placed either in up- 
right position, with the dorsal border of the transplanted disc corre- 
