628 THE PHYSIOLOGY OF REPRODUCTION 



parthenogenetic development, but the superior nutrition is 

 believed to have led to the production of females. 



The fact that in certain Crustacea a condition of herma- 

 phroditism can be induced by an external cause acting on a 

 sexually differentiated individual is discussed below in deahng 

 with latent characters. 



(2) Theories which assume that Sex-determination takes 



PLACE at the time OF FERTILISATION OR PREVIOUSLY TO 



Fertilisation 



Effect of Fertilisation, — ^While it seems certain that queen 

 and worker bees are developed from fertiUsed eggs under 

 different conditions of nutrition, the conclusion is now fairly 

 established that drones or male bees arise parthenogenetically 

 from unfertihsed eggs. If this view is correct, it clearly follows 

 that in bees the differentiation into female and male individuals 

 is brought about by the occurrence or non-occurrence of fertihsa- 

 tion. This theory of sex-determination in the bee was first 

 formulated by Dzierzon,^ and has since been accepted by 

 Weismann ^ and many other biologists, although some writers, 

 such as Beard,^ deny the conclusion that fertiUsation is capable 

 of exercising any such influence. 



In support of his contention Beard quotes an observation by 

 Weismann and Petrunkewitsch, showing that a drone egg may 

 occasionally undergo fertihsation. He also refers to the results 

 obtained by " bastardising " hives of bees through the intro- 

 duction of Itahan queens into colonies of Grerman workers and 

 drones, or of Grerman queens into ItaHan swarms.* In such a 

 bastard hive Dzierzon found a drone which appeared to be a 

 cross between a German and an Itahan bee, and which conse- 

 quently afforded evidence of a drone egg having been fertihsed. 

 This result led Dzierzon temporarily to doubt the truth of his 



' Dzierzon, " Uber die Befruohtung der Konigin," Eichstadt Bienen- 

 Zeitung, vol. i., 1845. 



^ Weismann, " Ueber die Parthenogenese der Bienen," Anat. Anz. , vol. v. 

 1900. 



^ Beard, "The Determination of Sex in Animal Development," Zool. 

 Jahrb., vol. xvi., 1902. 



* Von Siebold, Wahre Parthenogenesis bei SchmetterUngen und Bienen, 

 Leipzig, 1856. 



