279 
HERMAPHRODITISM AND OTHER ABNORMALITIES 
IN PEDICULUS HU MAN US. 
By D. KEILIN, Sc.D., and G. H. F. NUTTALL, F.R.S. 
[From the Quick Laboratory, University of Cambridge.) 
(With Plates XII-XVII and 28 Text-figures.) 
CONTENTS. 
PAGE 
Introduction ............. 279 
Sexual dimorphism in P. humanus ......... 280 
I. Hermaphroditism in P. humanus ........ 284 
Method of examination .......... 284 
Material.285 
Systematic description of 32 hermaphrodites ..... 286 
Description of Bacot’s 123 hermaphrodites ...... 295 
General characters of hermaphrodites in P. humanus .... 308 
Relation between primary and secondary sexual characters . . . 312 
Classification of hermaphrodites.312 
Fertility of hermaphrodites.313 
Frequency of hermaphroditism in P. humanus and its cause. . . 314 
(a) The percentage observed in' “wild” lice and other insects . . 314 
(h) The percentage observed in crosses between P. humanus races: 
capitis and corporis . . . . . . . . 315 
II. Some other abnormalities in P. humanus .318 
III. Conclusions.323 
Appendix I. Evidence proving that capitis may acquire all the characters of 
corporis ............. 324 
Appendix II. Evidence as to the opportunities for intermingling of capitis and 
corporis in nature ........... 325 
References ..327 
Explanation of Plates and key to lettering ....... 327 
INTRODUCTION. 
This paper is based on the study of a large material derived from various 
sources and containing a great number of abnormal specimens of Pediculus 
humanus , namely 155 hermaphrodites, besides abnormalities other than 
sexual which occur very rarely among insects. 
After having completed a systematic study of (a) specimens raised by us 
in the Quick Laboratory and of (b) specimens of “wild” lice that had reached 
