336 THE PHYSIOLOGY OF REPRODUCTION 



the sense that this term has been previously used," and that no internal 

 secretion is produced by interstitial tissue. Pezard 1 believes that 

 the internal secretion of the testes in birds is localised in the 

 germiuative cells or in the elements of Sertoli. 



Des Cilleuls 2 found that in the cock the appearance of interstitial 

 cells coincided with that of the secondary male characters, and that 

 they increase synchronously; also that the cock characters were 

 well marked at a time when the seminiferous tubules were still 

 embryonic. Thomsen 3 states that the secondary sexual characters 

 are established in the chick befo're hatching. Boring found that 

 interstitial connective tissue is very abundant in the testes of newly 

 hatched chicks, but, as mentioned above, there was no evidence of 

 secretory function. Reeves 4 observed interstitial tissue in cocks of 

 5|, 9, and 18 months. The whole question as to the seat of production 

 of the internal testicular secretion in birds still seems to be obscure. 



Goodale 5 has described the effects of removal of the testes in the 

 duck. The Rouen drake throughout most of the year has the nuptial 

 plumage which is assumed after the autumn moult. It is in striking 

 contrast to the plumage of the female, the head being green, and the 

 breast claret colour, and there are four curved tail feathers. The 

 breeding season ends in July when the drake assumes the 

 " eclipse " plumage which is very similar to that of the female. 

 The head becomes brown and the four tail sex feathers become 

 straight. The eclipse plumage lasts until the autumn moult in 

 October. In the mallard it continues somewhat longer. If, 

 however, castration is performed the eclipse plumage does not, 

 appear. This case seems somewhat similar to that of the hen- 

 feathered cocks described above. Shattock and Seligmann state 

 that when female wild duck assume the male plumage the spurious 

 males undergo the seasonal eclipse, although this may be incomplete 

 and aberrant. The same authors observe also that the periods of 

 activity and non-activity in the testis of the wild duck, as far as 

 spermatogenesis is concerned, do not correspond with seasonal changes 

 in the plumage. 



Duerden states that the red skin coloration of the cock ostriches 



1 P6zard, loc. cit. 



2 Des Cilleuls, " Api-opos du Determinisme des Caracteres Sexuel Secondaires 

 chez les Oiseaux," Compt. Rend, de la Soc. de Biol., vol. Ixxiii., 1912. 



3 Thomsen, "Die Differenzierung des Geschlechts und das Verhaltnis der 

 Geschlechten beim Huhnchen," Arch. f. Entwick.-Mech., vol. xxxi., 1911. 



4 Reeves, " On the Presence of Interstitial Cells in the Chicken's Testis," 

 Anat. Record, vol. ix., 1915. 



6 Goodale, "Some Eesults of Castration in Ducks," Biol. EidL, vol. xx., 

 1910 ; Gonadectomy, Carnegie Inst. (Washington) Pub. No. 243, 1916. See also 

 Sfcattock and Seligmann, " Observations made to ascertain whether any Relation 

 subsists between the Seasonal Assumption of the Eclipse Plumage in the 

 Mallard and the Functions of the Testicle," Proc. Zool. Soc., 1914. 



