666 THE PHYSIOLOGY OF REPRODUCTION 



and decreases as these diminish." ^ Certain further experiments with 

 unfertilised ova of the same species seem to show that " the more 

 abundant the metabolism (Stoffwechsel) and the nutrition, the 

 greater vthe tendency to the production of females." In the normal 

 condition males only were produced as a result of 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 hermaphroditism 

 can be induced by an external cause acting on a sexually differentiated 

 individual is discussed below in dealing with latent characters, and 

 further observations of a comparable character and relating to 

 other animals are also considered. 



(2) Theokies which assume that Sex - detekmination takes 



PLACE AT THE TIME OF FERTILISATION OR PEEVIOUSLY 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 tggs. 

 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 fertilisation. 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 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 introduction of 

 Italian queens into colonies of German workers and drones, or of 

 German queens into Italian swarms.^ In such' a bastard hive Dzierzon 

 found a drone which appeared to be a cross between a German and 

 an Italian bee, and which consequently afforded evidence of a drone 

 egg having been fertilised. This result led Dzierzon temporarily to 

 doubt the truth of his hypothesis, but he subsequently accepted the 



1 Translated by Geddes and Thomson. 



2 Dzierzon, " tJber die Befruchtung der Konigin," Eickstadt Bienen-Zeiiung, 

 vol. i., 1845. 



3 Weismann, "Ueber die Parthenogenese der Bienen,'' Anat. Am., vol. v., 

 1900. 



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

 vol. xvi., 1902. 



^ Von Siebold, M'ahre Parthenogenesis bei Sehmetterlmgen imd Bienen, 

 Leipzig, 1856. 



