282 LEIGH HOADLEY. 



grafted to another larva of approximately the same age. In 

 such experiments, the grafted parts continue to develop while the 

 graft is nourished and relieved of its excretions by the host. The 

 differentiation of the organs of the host, which are developing 

 simultaneously with those of the transplanted part, must, how- 

 ever, affect the differentiation of the transplant to a greater or 

 lesser degree. 



The ideal conditions for a transplantation in which it is desired 

 to determine the independent power of growth and differentiation 

 of the part, would be in a location where there are no nerves from 

 the host, where there is no differentiation of host tissue to 

 influence the grafted part, and where there is a sufficient supply 

 of blood vessels to insure nutrition and the ability to excrete 

 waste products on the part of the transplant. This must be in a 

 rapidly growing tissue which is capable of repair, and such as will 

 react to foreign tissue with rapid incorporation and a host of 

 capillaries. The chorio-allantoic membrane of the chick furnishes 

 such conditions as has been pointed out by Murphy (1913), 

 Danchakoff (1916), Kiyono (1917), Minoura (1921), and Atter- 

 bury (1923). 



It is my intention to attack the problems of independent growth 

 and differentiation by the isolation and transplantation of the 

 various primordia of the chick embryo to the chorio-allantoic 

 membrane. A general survey of the field has already been made 

 with a variety of tissues and has yielded promising results. For 

 instance, when a cross section of the body of the thirty-six or 

 forty-eight hour chick is transplanted, the grafts obtained show 

 that cartilage, bone, muscle, nervous tissue, and mesonephros 

 grow 'well. In one case of transplantation of the primitive 

 streak, nephrogenous tissue is found to be present. In many 

 cases of such grafts of cross sections of the body, small buds of 

 the feather germs form and grow well; they receive a rich 

 vascular supply. The present paper is confined to the organs of 

 special sense, i.e., the eye, nasal region, otic region, and one 

 example of brain tissue, the mesencephalon. The mesencephalon 

 was selected because of its close association with the eye, and 

 because of its high degree of differentiation in the birds. Other 

 parts will be considered in later papers. 



