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 dealing 

 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 fertilised eggs under 

 different conditions of nutrition, the conclusion is now fairly 

 established that drones or male bees arise parthenogenetically 

 from unfertilised 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 fertilisa- 

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

 formulated by Dzierzon, 1 and has since been accepted by 

 Weismann 2 and many other biologists, although some writers, 

 such as Beard, 3 deny the conclusion that fertilisation 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 fertilisation. He also refers to the results 

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

 duction of Italian queens into colonies of German workers and 

 drones, or of German queens into Italian swarms. 4 In such a 

 bastard hive Dzierzon found a drone which appeared to be a 

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

 quently afforded evidence of a drone egg having been fertilised. 

 This result led Dzierzon temporarily to doubt the truth of his 



1 Dzierzon, " Uber die Befruchtung der Konigin," Eichstadt Bienen- 

 Zeitung, vol. i., 1845. 



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

 1900. 



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

 Jahrb., vol. xvi., 1902. 



4 Von Siebold, Wahre Parthenogenesis bei Schmetterlingen und Bienen, 

 Leipzig, 1856. 



