Volume IX DECEMBER, 1919 No. 1. 



STUDIES IN THE HYBRID BISTONINAE. 



IV. CONCERNING THE SEX AND RELATED PROBLEMS. 



By J. W. HESLOP HARRISON, D.Sc. 



(With PI. I and 10 Text-figures.) 

 CONTENTS. 



PAGE 



Introductory 1 



On the wholly male broods ........... 5 



Inbreeding and its effects in inducing the appearance of females in broods which, 



according to expectation, should have been unisexual and male ... 13 

 The problem of the single female in the cross between N. zonaria female and a 



(P . pomonaria ^ x P. isabellae'^) ra&le ........ 16 



On the preponderance of males in the P. pomonaria ^ x L. hirtaria $ broods when 



the L. hirtaria were of Scotch origin ........ 19 



On the status of the P. pomonaria .^ x L. hybrid pilzii ^ brood .... 20 



On the causes of the development of such intersexes 33 



Description of the genitalia of one of the P. pomonaria x P. lapponaria intersexes . 35 



Introductory. 



Experiments designed to secure hybrids in the Geometrid Sub- 

 family Bistoninae have had sex results presenting unforeseen and 

 abnormal occurrences of such diverse types that, whenever the general 

 results of the experiments have been discussed, the sex problems have 

 been reserved for special treatment; this treatment it is proposed to 

 give in the present paper. Before proceeding with the discussion, 

 however, as much of it depends on the phylogenetic relationship of 

 the species concerned a brief sketch of the phylogeny must be given 

 here. 



As I have pointed out elsewhere the Geometrid Subfamily Bistoninae, 

 on the structure of the genital armature combined with other more or 

 less • important characters, can be divided into two sections: (1) the 



Journ. of Gen. ix 1 



