72 On the Sterility of the Tortoiseshell Tom Cat 



colour cannot have been due to sterility, whereas it is not impossible 

 that the abnormal transmission of a sex-limited colour-factor to a male 

 may sometimes cause the animal to be sterile, and in other cases not 

 have this effect, just as i-etention of the testes in the abdomen does not 

 always lead to total sterility. In this connexion it is interesting that 

 similar phenomena are said to be found in breeds of fowls, such as the 

 Sebright, in which the male may be hen-feathered. It is supposed by 

 some fanciers that in these breeds completely hen-feathered cocks are 

 not infrequently sterile, and in consequence cocks which are only 

 partially hen-feathered are generally used for breeding. Prof Punnett 

 has kindly given us sections of a testis of a completely hen-feathered 

 cock, extracted from the cross Sebright hen x Hamburgh cock, in which 

 ' the tubules contain no trace of spermatogenesis, but are in general 

 similar to those of the tortoiseshell tom cat (Fig. 6). They differ chiefly 

 in being lined with many cells with rather small nuclei, instead of the 

 comparatively few large cells — which we have compared with Sertoli 

 cells — found in the cat. There is also a somewhat increased amount of 

 interstitial tissue, a fact which would be of considerable interest in 

 a cock with the female type of plumage if it wore certain that the 

 interstitial tissue of birds had a secretory function like that of Mammals. 

 The interstitial tissue of the normal fowl is smaller in amount than 

 in the mammals, and it is maintained by Miss A. M. Boring {Biol. Bull. 

 XXIII. 1912, p. l^l) that it consists simply of connective tissue, and has 

 no secretory function. The testis of the hen-feathered cock supports 

 her conclusion to this extent, that the interstitial cells contain neither 

 the vacuoles nor the secretory granules which are so conspicuous in the 

 cat (Fig. 6, i.t). The tissue is, however, not by any means entirely 

 fibrous, but seems to consist of cells with fibres running among them 

 and it is doubtful whether it can properly be described as connective 

 tissue. In any case, the testis of the hen-feathered cock supports the 

 conclusion that the sterility is a consequence of the possession of an 

 abnormal hereditary factor, for hen-feathering is undoubtedly due to 

 such an inherited factor, and is not a mere consequence of sterility, so 

 that the cases of the tortoiseshell cat and hen-feathered cock taken 

 together suggest that when a male animal receives a factor, either 

 normally or through failure of the normal sex-limited transmission, 

 which causes it to assume characters proper to the female, there is 

 a tendency for sterility to appear. 



