DIMORPHISM AND POLYMORPHISM 36 1 



Siebold,* and more recently by Kraepelin — being furnished 

 by bees. The male and female secondary sexual characters are 

 combined in the most wonderful manner in these hermaphrodite 

 forms : in some bees, the right side was fetnale and the left tnale ; 

 in others, the anterior half of the body was male and the poste- 

 rior female ; while in others, again, the entire trunk was male 

 and one side of the head female. As Leuckart remarks, 'the 

 male and female characters ' in these hermaphrodite bees ' have 

 been intermingled in the most varied and unsystematic manner, 

 so that it is difficult to discover two individuals with perfectly 

 similar characteristics.' 



We are indebted to Kraepelin for an excellent account of 

 the external sexual parts in these hermaphrodite bees,t in- 

 cluding the copulatory apparatus. His description shows that 

 the blending of the male and female characters even affects 

 very small parts. It not only often happens, for instance, 

 that half the entire stinging apparatus of the left side is 

 female, while an intromittent organ is developed on the right, 

 but certain chitinous plates on the ventral side of the last 

 abdominal segment, which is almost male in character, also 

 display a distinct tendency to take on the form of the corre- 

 sponding plates of the female stinging apparatus ; in other 

 words, these chitinous plates are intermediate in form between 

 those of the male and female. Their formation must therefore 

 have been controlled by a combination of ' male ' and ' female ' 

 determinants. It would be incredible that these harmonising 

 determinants could have met together at the right point in the 

 extremely complex combination of determinants in the germ- 

 plasm if they had not been arranged together from the first, and 

 if an arrangement of male and female double determinants had 

 not previously existed in every such region of the germ-plasm, 

 so that they reached the corresponding part of the body together 

 in the course of ontogeny, either the male or the female half 

 then becoming active. 



In the determination of sex in the normal development of bees, 

 all these somatic double determinants must be correspondingly 

 determined. We do not know to what factor the prevention of 

 the determination of sex in a similar manner in the formation 



* C. Th. von Siebold, 'Zeitschrift fur vvissenchaftliche Zoologie,' Bd. 

 xiv., 1864, p. 73. 



t Kraepelin, ' Zeitschr. f. wiss. Zoologie,' Bd. xxiii., 1873, p. 326. 



