14 TADACHIKA MINOURA 



disappears, usually before hatching. Although the degeneration 

 of the right ovary in birds has been known for a long time, there 

 are, curiously enough, no detailed studies upon the matter, so 

 that there is in the literature no information available concerning 

 the degree of development attained by the right ovary, the time 

 at which it begins to retrogress, or the manner and degree of 

 its retrogression. From my work I am able to add some 

 details to the facts already known. After the stage when the 

 difference between the two ovaries becomes apparent, the right 

 ovary shows some slight increase in length, usually not more 

 than 50 per cent. This continues until about the end of the 

 second week of incubation. From this time on, a process of 

 degeneration is manifested in the right ovary by its decrease in 

 length and change in position. Up to the sixth or seventh day 

 the two ovaries lie nearly parallel to the longitudinal axis of the 

 body. After the right ovary has begun to degenerate, its ante- 

 rior end tends to incline more and more to the right side, so as 

 to assume an oblique position with reference to the right wolffian 

 body. The outlines of the ovary gradually become less and less 

 distinct; this change is more marked on the medial and anterior 

 margins of the ovary. Meantime the volume of the ovary 

 continually diminishes so that it becomes more and more slender. 

 In the case of several 18 to 20-day-old females, the right ovary 

 was reduced to a flattened membranous body, although the 

 fading outlines could still be determined. The final disappear- 

 ance of the right ovary occurs in general at about the age of 18 

 days; individual differences, of course, exist. The data on the 

 length of the two ovaries at various stages of development are 

 given in table 4. 



c. Wolffian ducts. It has generally been believed that in the 

 female chick embryo the wolffian ducts degenerate simulta- 

 neously with the wolffian bodies before hatching, or, at least, at 

 some later time. The recent observations of Goodale ('16) 

 Boring and Pearl ('18), however, show that this belief is erro- 

 neous. Goodale states that "apparently the wolffian duct and 

 body may not always degenerate in the female." Boring and 

 Pearl dissected a number of newly hatched chicks or chicks 



