1120 



SUBMAMMALIAN VERTEBRATES 



feather type also in those cases in which 

 no right rudimentary gonad develops 

 (Domm, 1939). Parkes (1952) has pointed 

 out that the feather development of the 

 Brown Leghorn capon may be used suc- 

 cessfully to measure the duration of action 

 of different estrogens. 



Witschi (1955 for review) has analyzed 

 a peculiar phenomenon of determination of 

 feather coloring which exists in certain 

 species. During the nonbreeding season 

 males and females of the genera Euplectes, 

 Steganura and Quelea have the hen plum- 

 age. Just before the breeding season the 

 male passes through a partial molt, and 

 the new plumage is the brightly colored 

 cock plumage. Castration of the male does 

 not affect the changing of the plumage from 

 eclipse to nuptial plumage, whereas ovari- 

 ectomy of the female causes her to go 

 through the same phases as the male or 

 the castrated male. These experiments 

 proved that plumage color was independent 

 of androgens but, nevertheless, showed cy- 

 clic changes. Experimentally, Witschi dem- 

 onstrated that LH injections will cause color 

 changes of newly formed feathers in these 

 species. The response is specific and sensi- 

 tive enough to be used for bioassays of Lli 

 (see addendum). In intact Euplectes, color 

 changes in plumage and bill occur together 

 under normal conditions. The feather color 

 is a reflection of the LH directly, whereas 

 the bill color is a reflection of androgen se- 

 cretion by the testes under influence of LH. 

 In wydahs (Steganura paradise a) , LH de- 

 termines bill color directly. The lack of 

 cock plumage in normal females is the re- 

 sult of estrogen inhibition of male plumage 

 as Witschi (1937) demonstrated experimen- 

 tally. 



2. Androgen. Evidence for the secretion 

 of androgen by the avian ovary can be 

 found in the red vascular com!) of the 

 chicken before and during egg production, 

 in the yellow bill and the stimulated vasa 

 deferentia of the female starling {Sturnus 

 V. vulgaris) during her reproductive season 

 (Witschi and Fugo, 1940). These characters 

 of the starling are stimulated by androgens 

 only and not by estrogen or progesterone 

 (Fugo and Witschi, 1940). 



Benoit (1950a), Taber (1951), and Mar- 



shall and Coombs (1957) have suggested 

 that the interstitial cells of the ovary (Be- 

 noit, 1950a; Taber, 1951), or, more specifi- 

 cally, the ovarian interstitial cells arising 

 from the connective tissue cells of the ovar- 

 ian stroma (Marshall and Coombs, 1957) 

 are the source of androgen in female birds. 



Some of the effects that androgens can 

 have on blood composition have been dis- 

 cussed in a previous section of this chapter. 

 Their main function in female birds may be 

 to act synergistically with estrogen in the 

 stimulation of the oviduct. In chickens an- 

 drogen acts synergistically with estrogen to 

 increase calcium retention (Common, Maw 

 and Jowsey, 1953.) and to increase endosteal 

 bone formation (Jowsey, Oliver, Maw and 

 Common, 1953) ; the interaction may be 

 caused by increased Ca absorption from the 

 gut caused by androgen combined with the 

 increased formation of endosteal bone 

 caused by estrogen (Jowsey, Oliver, Maw 

 and Common, 1953). 



.3. Progesterone. Evidence that the avian 

 ovary secretes progesterone is provided by 

 the detection of a biologically active pro- 

 gestin in the blood of laying and nonlaying 

 hens (Fraps, Hooker and Forbes, 1948, 

 1949 1 and by the chemical identification 

 of progesterone in extracts from ovaries of 

 laying hens (Layne, Common, Maw and 

 Fraps, 1957). Progesterone (5 fig. per 100 

 ml.) as such was detected in the blood of 

 laying hens when loss of progesterone in 

 the peripheral tissue was circumvented 

 (Lytle and Lorenz, 1958). The source of 

 jn-ogesterone in the ovary has not been 

 established. In all probability it is not the 

 ruptured follicle, because the amount of 

 progesterone in it is small. Fraps (1955) 

 proposed that the maturing follicle is a pos- 

 sible, but not the exclusive, source of pro- 

 gesterone, whereas Marshall and Coombs 

 (1957) favored certain amorphous noncel- 

 lular aggregations of cells of cholesterol- 

 positive lipid in atretic follicles. Neither of 

 these tissues has been proven (or disproven) 

 to be the source of progesterone. 



Whatever the source of progesterone may 

 be, it seems to function largely in regulat- 

 ing the ovulatory cycle, at least in the 

 chicken (a topic discussed under endocrine 

 regulation of ovarian activity) ; progester- 



