18 TADACHIKA MINOURA 



lumen near the cloaca. This differentiation of the posterior 

 end of the right miillerian duct of the female does not occur in 

 the male, even to the slightest degree. In the second place, 

 the degeneration was found to occur somewhat irregularly. In 

 many cases, in embryos as young as eleven or twelve days, the 

 right duct was already in an advanced state of degeneration. On 

 the other hand, seventeen-day-old embryos may retain more 

 than half of the duct intact. 



e. Range of size variation in normal testes. Data on the normal 

 size variation of the reproductive glands and ducts in birds are 

 rather scanty. Almost no attention has been paid to the varia- 

 tion in the size of the two testes, it having apparently been 

 assumed that the testes of the two sides develop equally. 



Etzold ('91) measured the testes of the sparrow and found 

 that the left testis is larger than the right one. Swift ('16) 

 made the same observation in the chick embryo at the age of six 

 days and noticed further that there are more germ cells in the 

 left testis. Riddle ('17) studied this matter very carefully in 

 the pigeon and found that the right testis normally weighs more 

 than the left testis. In regard to the shape of the two testes, 

 he states that ''the left is thinner and more elongated, the right 

 shorter and thicker." In regard to this difference in shape 

 between the two testes. Riddle made an interesting suggestion: 

 ''This difference in form is perhaps not without interest since 

 the only persistent gonad in the female — that of the left side — is 

 characteristically 'thin' and 'long.' The testis that develops on 

 this side is similarly characterized as compared with its mate 

 of the right side." Riddle also determined the weight of the 

 testes in the fowl, but owing to the small number of individuals 

 investigated, the results were indefinite. 



I have collected some data on the development, size, and shape 

 of the two testes in chick embryos. Both testes develop rapidly 

 until about the eighteenth day, after which their rate of devel- 

 opment diminishes. They are about equal in size, or the left 

 one may be a little larger. This inequality in the size of the two 

 testes appears more clearly in the earlier stages of development 

 and tends to disappear later. In the majority of cases, the 



