ZOOLOGY: R. G. HARRISON 
247 
wherever or in whatever position implanted, but they also show that 
its laterality may be affected by its new surroundings. There are many 
instances o imperfect development, and of total absorption of the trans- 
planted tissue, especially in the case of the heterotopic transplantations. 
Also, as has been observed before (Braus,^ Harrison,^) supernumerary 
appendages often arise after transplantation, just as in regenerating 
limbs under certain conditions (Tornier,' Delia Valle.)^ 
In the orthotopic operations the transplanted limb, whatever its 
form, usually becomes functional, while in the heterotopic this is rarely 
the case and the function is never perfect. Functional activity, to- 
gether with the superior potency of the norma surroundings in influ- 
encing the development of the limb, renders the results of orthotopic 
transplantation, in so far as they bear on the problem of laterality, 
more complicated and difficult to interpret than the heterotopic. Never- 
theless the following fundamenta rules underlie the determination of 
laterality in both cases. 
Rule 1. A bud that is not inverted (dorso-dorsal) retains its original 
laterality whether implanted on the same or on the opposite side of 
the body. 
Rule 2r An inverted bud (dorso-ventral) has its laterality reversed 
whether implanted on the same or on the opposite side. 
Rule 3. When double or twin limbs arise the original one (the one 
first to begin its development) has its laterality fixed in accordance 
with the above rules, while the other is the mirror image of the first. 
In the heterotopic transplantations the tissue is very often resorbed 
or the appendages which arise are rudimentary or imperfect (56%). 
Probably vascularization is not so good and innervation is incomplete. 
Reduplications were produced in all of the four combinations. 
In the orthotopic transplantations only about 18% of the limbs 
were rudimentary or imperfect, the rest being either fully developed 
reduplications or normal limbs. Double limbs were obtained frequently 
in two of the combinations (heteropleural dorso-dorsal and homopleural 
dorso-ventral) and were very rare in the other two. Other modifica- 
tions also occurred. The results were as follows: 
1. Homopleural dorso-dorsal grafts developed normally though at 
first very slightly retarded. Rule 1; 6 cases (100%).^ 
2. Homopleural dorso-ventral grafts resulted in (a) A single limb of 
reversed lateraHty (a structurally and functionally perfect right limb 
on the left side). Rule 2; one case only (4.3%). (b) Reduplicated 
limbs. Rule 3; 16 cases (69.6%). (c) Typical non reversed limbs 
which began their development by growing in an abnormal direction, 
