1906.] ON THE OSTEOLOCJY OF THE TRACHEOPHONE PASSERES. 133 



-Zool. vol. ii. p. 543)*, and based on his work on chromosomes. 

 We may suppose, however, the two " idiochvomosomes " (or 

 " heterotropic chromosomes ") in the female before reduction to 

 bear the male and female sex-determinants respectively, while in 

 the male the female-bearing chromosome is reduced or absent. 

 Then in the female we shall have segregation of the sex- 

 determinants at the maturation-divisions, and we may suppose 

 that female-bearing eggs are fertilized by male-bearing sperma- 

 tozoa, giving females, the male-bearing egg being fertilized by 

 the spermatozoon which has no "heterotropic" chromosome. 

 This is in full accord with the hypothesis suggested by the 

 behaviour of the var. lacticolor t. 



EXPLANATION OF PLATE VIIL 



Fig. 1. Angerona prunaria, ^ : p. 125. 



2. Heterozygote prunaria X sordiata, <? : p. 128. 



3. Pure var. sordiata, $ : p. 128. 



4. Abraxas grossulariata, $ : p. 129. 



5. Var. lacticolor, ? : p. 129. 



2, Contributions to the Osteology of Birds. — Part YIILJ 

 The " Tracbeophone " Passeres ; wikh Remarks on 

 Families allied thereto. By W. P. Pyckaft, F.Z.S., 

 A.L.S., &c. 



[Received December 28, 1905.] 



(Text-figures 49-52.) 



i. Introductory Remarks. 



In the following pages I have endeavoured to describe the main 

 features of the Osteology of the Tracbeophone Passeres ; and, 

 further, I have striven to embrace in these remarks such other 

 anatomical facts as may seem to bear trustworthy evidence as to the 

 systematic position of the group. 



The " Tracheophonete " seem to form a natural group, allied on 

 the one hand to the Euryleemida?, Cotingid?e, and Philepittidas, 

 and on the other to the Tyrannid^e and Pittid^e : details on this 

 point will be found later (p. 158). 



This paper is by no means so complete as I could have wished, 

 inasmuch as many genera yet remain to be examined. The 

 position ascribed to some of these at the present day is open to 

 grave suspicion ; but these doubts cannot be set at rest until 

 skeletons and birds in spirit are sent home in place of skins. 



* Also 'Science,' xxii. 1905, p. 500. 



t Since this paper was written, Wilson has suggested an explanation of his results 

 identical with that outlined here (Journ. Exp. Zool. vol. iii., Feb. 1906). 

 X For Part VII. see P. Z. 8. 1905, vol. ii. p. 30. 



