722 On Central Tail-feathers in Bird-of -Paradise. [Ibis, 



cover as one of the two normal. Perhaps there is some 

 reason for scepticism about the naturahiess of the origin in 

 this case. 



How is such an abnormality to be explained? Vie do not 

 gain very much by using the word "'atavism" (although we 

 could mention birds with more than twelve tail-feathers), 

 because undoubtedly the thread form of the inner feathers is 

 a character newly acquired in tlie family Paradiseidae. Of 

 course we do not know whether the abnormality is hereditary 

 (as, for instance, poIydactyly). It might be supposed that 

 the enlarged number of thread-feathers was only the result 

 of an abnormal or incomplete moulting, and therefore an 

 accidental and individual deviation. The insertion of the 

 feathers in the doubled knob, however, make, as it seems to 

 me, this hypothesis highly improbable. The case is some- 

 what more complicated by the symmetr}' of the doubling 

 and the inequality of the normal and sujoernumerary thread- 

 feathers on each side. Like other authors on this subject, 

 I am of tbe opinion that in similar cases of doubling, not 

 easily explnined by external inHuences, we recall the vege- 

 tative mode of division, so largely spread in lower animals, 

 revived, perhaps, after a damage at an embryonic stage. 

 Regarding the question, whether such a vegetative augmen- 

 tation of the number of rectrices be not a very rare 

 exception, we must keep in mind that with birds «ith 

 equal tail-feathers such an abnormal increase will noi often 

 be detected. 



In reference to the above paper, Lord Eothschild wishes 

 to remark that the duplication of the central pair of 

 rectrices in the Paradiseidse is not so rare as supposed. 

 Besides several previous records in the literature from 

 various sources, he wishes to say that the Tring Museum 

 possesses a skin of Diphyllodes magnifica with four fully- 

 developed central rectrices. 



