1906.] ox THE OSTEOLOGY OF THE TRACHEOPHONE PASSERES. 133 



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

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

 " heterotropic chromosomes ") in the female before reduction to 

 bear the male and female sex-determinants respectively, Avhile 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 

 l)ehaviour of the var. lacticolor f. 



EXPLANATION OF PLATE VIIL 



Fig. 1. Angerona prunaria, $ -. p. 125. 



2. Hetei-ozygote prunaria X sordiata, S : P. 128. 



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



4. Abraxas c/rossulariata, $ : p. 129. 



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



2. Contributions to the Osteology of Birds.— Part VIII.J 

 The " Tracheophone " Passeres ; with Pemarks 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 Tracheophone 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 " Tracheophoneaj " seem to form a natui-al group, allied on 

 the one hand to the Eurylfemida?, Ootingida?, and Philepittid^, 

 and on the other to the Tyrannidfe and Pittidse : 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. 



* Ali50 ' 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. S. 1905, vol. ii. p. 30. 



