12 TADACHIKA MINOURA 



As shown in table 3 the grafts produced the most effect when 

 they were implanted on the embryos during the second week of 

 incubation, that is, from the seventh to the thirteenth days of 

 incubation. Especially 8-, 9-, 10-, and 11-day old embryos were 

 found to be most fmvorable for the purpose of the experiments. 

 The facts revealed by table 3 are not difficult to understand. In 

 embryos younger than five days the allantoic circulation is not 

 sufficiently well estabhshed to permit of vascular conneqtions 

 with the graft; grafts inplanted on such young embryos therefore 

 die from a lack of blood supply. In the case of embryos more 

 than two weeks old it is probable that a resistance to foreign 

 tissues has been developed and that such embryos are thereby 

 enabled to destroy the grafts. Murphy. ('14) pointed out that 

 a defensive mechanism against foreign tissue develops in chick 

 embryos at about the time of hatching. He noted a sudden 

 appearance of lymphoid cells around the graft at this time and 

 ascribed the function of the destruction of foreign tissue to these 

 cells, considering them to be similar in function to the cells of 

 the spleen and of bone-marrow. My results are in general 

 agreement with Murphy's statements except that in the case of 

 my experiments I am unable to determine whether the resistance 

 to foreign tissue appears suddenly or develops gradually. It is, 

 however, certain that embryos more than two w^eeks old are 

 unfavorable for the implantation of foreign tissue. 



ANATOMICAL STUDY OF THE EMBRYOS 



We may now proceed to a consideration of the effects cf the 

 gonad grafts on the anatomy of the chick embryos. In this 

 paper only the gross anatomy of the affected embryos will 

 be described, the histological findings being reserved for a subse- 

 quent paper. 



1 . Development of sex-glands and sex-duds in normal embryos 



Before passing to a consideration of the experimental results, 

 it is necessary to review the normal development of the sex- 

 glands and sex-ducts in the chick, with special reference to those 

 points concerned in the present experiments. 



