EFFECTS OF GONAD GRAFTS IN CHICKS 19 



difference in length of the two testes ranges between 0.1 and 0.3 

 mm. In normal embryos the difference does not exceed 0.5 mm. 

 The shape of the two testes is similar to that described by Riddle 

 for the pigeon. The left testis is more elongated than the right 

 one; the right one is shorter and in a few cases thicker. But in 

 general I cannot say that the right testis is the larger of the two. 

 Owing to the nature of my experiments, I could not remove the 

 testes for the purpose of weighing them, but I am inclined to 

 think that in the chick the left testis is larger and weighs more 

 than the right one. The data concerning the lengths of the 

 right and left testes of the chick are given in table 5. 



2. Development of sex-glands and sex-ducts in grafted embryos 



a. General resume of the experimental results. Nearly one 

 thousand eggs were used in the experiments. Of these about 

 three hundred were incubated as controls and about one hundred 

 more were used for grafting organs other than gonads. The 

 remaining eggs served for the implantation of pieces of ovary 

 and testis. In all 187 embryos on which gonad grafts had been 

 implanted were living at the time of examination, and these 

 furnish the materials for this part of the paper. 



The 187 embryos obtained in the experiments are classified 

 in table 6. In this table and elsewhere testis graft means that 

 a piece of testis had been grafted on the membranes of the embryo 

 in question and ovary graft that a piece of ovary had been so 

 grafted. Male-type embryos are those which have predomi- 

 nantly male anatomical characteristics. The normal male at or 

 near the time of hatching is distinguished by the following 

 characters: there are two testes of equal size; the testes are 

 elongated in form and smooth in texture, and there are no 

 miillerian ducts (figs. 7, 8) . Affected embryos whose gonads and 

 ducts approach this description are hence regarded as male.-type 

 embryos. Female-type embryos are those whose gonads and 

 ducts resemble those of the normal female. The characteristics 

 of the normal female at or near the time of hatching are: the 

 right ovary is absent; the left one is larger and broader than 

 either testis; its surface is commonly rough in texture; the left 



