274 INTERNAL SECRETIONS 



right side and the organ which developed in the castrated hens 

 on the left side ; according to Goodale there may have been one. 

 In castrated ducks, which showed a similar change from male 

 to female plumage, Goodale found this organ only once. 



The observations of Goodale make it highly probable that 

 there was in his experiments a periodic change in hormone- 

 production. "It is evident that if the organs are concerned 

 with the changes, there must be some change in the activity 

 of the organs either preceding the changes in plumage or 

 accompanying them" (Goodale, 1916, p. 292). 



Goodale mentions that these organs are very likely identical 

 with the bodies described by various observers in cock-feathered 

 females. We shall return to this important question in 

 Chapter IX., when discussing some experiments by Pezard and 

 Zawadowsky. The observations of Goodale leave no doubt 

 that production of sexual hormones or production of hormones 

 identical with the latter is possible without any ovum being 

 present in the body. 



A thorough investigation into the follicular development 

 and the seat of production of sex hormones in birds has been 

 made by certain American authors, especially by Pearl and 

 Boring (1917, 1918 a, 1918 b). According to these observers 

 there is during follicular development a complete degeneration 

 of the granulosa, whereas the theca interna undergoes hyper- 

 trophy. The interstitial cells are derived from the theca interna. 

 In the theca interna are located also groups or nests of epithelial 

 cells, which are very different from the usual glandular inter- 

 stitial cells. These cells, which they call "lutear cells, " are about 

 three times as large as the interstitial cells; their nucleus is 

 bigger, the cytoplasm is usually clear and vacuolated in 

 appearance; a few acidophile granules are occasionally present, 

 while the real interstitial cells are crowded with granules. 

 When follicular atresia is completed the big clear cells contain 

 a yellow pigment, and this is why the authors call these cells 

 lutear cells. There is, according to Boring and Pearl, no 

 difference between an atretic follicle and a corpus luteum; 

 "they are practically identical in the hen" (Pearl and Boring, 

 19 18 a, p. 15). The lutear cells of the corpus luteum also are 

 formed from the cells of the theca interna. 



The interstitial cells in the ovary of birds are homologous 

 with those in the ovary of mammals; according to Boring and 



