TADACHIKA MINOURA 



Kiyono ('17) grafted tissues and organs on chick and duck 

 embryos and classfied them according to their capacities for 

 growth into three groups, the first named having the greatest 

 capacity: 1) connective tissue, cartilage, skin; 2) muscle, mucous 

 membrane of the alimentarj^ and respiratory tracts; 3) kidney, 

 eye, liver, nervous tissue, and glands. He stated that tissues and 

 organs having simple functions grow most readily when- grafted, 

 while those having more complex structure and functions grow 

 less easily. This statement was verified in my experiments, 

 since I found that ovary and testis grafts have a lower growth 

 capacity than thymus, liver, and spleen grafts. 



TABLE 2 



Comparison of sizes attained by testis and ovary grafts 



b. Histological study. The histological structure of sectioned 

 grafts was studied with great interest. In general, sections of 

 the grafts exhibited four distinct regions arranged concentrically 

 (fig. A). 



1. Chorio-allantoic membrane. The graft is encircled by the 

 chorio-allantoic membrane. The external layer of this mem- 

 brane consists of the ectoderm of the chorion; it passes over the 

 outer surface of the graft (fig. A, ec). The internal layer passing 

 beneath the graft is the entoderm of the allantois (fig. A, ea). 

 Both ectodermal and entodermal membranes are very thin layers, 

 one cell in thickness. Between the ectoderm and entoderm is 

 the mesoderm, composed of the fused mesoderms of both chorion 



