THE FACTORS WHICH DETERMINE SEX 667 



interpretation of von Siebold, who suggested that the queen which 

 had given rise to the apparently bastard drone was herself of impure 

 descent, and that in reality the egg had not been fertilised. A 

 further exceptional case has been recorded by Perez/ who found that 

 a considerable number of male bees produced by an Italian queen 

 which had been fertilised by a French drone appeared to be of mixed 

 blood. This result, which is admittedly unusual, has been explained 

 by Sanson^ as due to "reversion," and Morgan has pointed out 

 that the hybrid drones may conceivably have arisen from hybrid 

 workers which sometimes lay eggs, and further that male bees are 

 often very variable in their characters. Either of these explanations 

 would appear to be possible. 



Moreover, the later observations of Petrunkewitsch,^ showing 

 that sperm nuclei are not l^ound in drone eggs whereas they are 

 commonly met with in worker eggs, supply an important con:Srmation 

 of Dzierzon's hypothesis. 



Attempts to extend this hypothesis to other hymenopterous 

 insects have not been so satisfactory, though it seems, as a general 

 rule, to hold good for ants. There are instances on record, however, 

 in which worker ants have developed from parthenogenetic ova, and 

 other exceptional cases have been stated to occur.* 



Among the Tenthredinidse or sawflies also the unfertilised eggs 

 commonly develop into males, but this is by no means invariable. 

 Thus in some forms fertile parthenogenetic females only have been 

 known to arise for many generations in succession without the 

 appearance of males.^ 



In the parthenogenetic Rotifer, Hydatina, Maupas ^ has adduced 

 strong evidence that if the parthenogenetic male eggs are fertilised 

 they are thereby converted into "winter" eggs which give rise solely 

 to females. If this is so (and Maupas's conclusions are now generally 

 accepted), it is a clear instance of fertilisation altering the sex of 



1 Perez, " M^moire sur la Ponte de TAbeille . reine et la Th6orie de 

 Dzierzon," Annales des Sciences Nat., vol. v., 1878. 



2 Sanson, "Note sur la Partli6nogfen6se ctez les Abeilles," Annales des 

 Sciences Nat., vol. v., 1878. 



^ Petrunkewitsch, " Die Eiolitungskorper und ihr Schicksal im befruchteten 

 und unbefruchteten Bienenei," Zool. Jahrh., vol. xiv., 1901. "Das Sehieksal 

 der Riehtungskorper im Drohnenei," Zool. Jahrh., vol. xvii., 1902. 



* Wheeler, "The Origin of Female and Worker Ants from the' Eggs of 

 Parthenogenetic Workers," Science, vol. xviii., 1903. 



'' Doncaster, " On the Maturation of the Unfertilised Egg and the Fate of 

 the Polar Bodies in the Tenthredinidw," Quar. Jour. Micr. Science, vol. xlix., 1906. 



" Maupas, " Sur la Multiplication et la F6condation de FHydatina senta," 

 C. R. de VAcad. des Sci, vol. cxi., 1890. " Sur la F^oondation de THydatina 

 senta," G. R. de I' Acad, des Sci, vol. cxi., 1890. "Sur la Deterniinisme de la 

 Sexuality chez Hydatina senta," 0. R. de I' Acad, des Sci., vol. cxiii., 1891. Lenssen, 

 Contribution a I'^^tude du D6veloppement, etc., chez I'Hydatina, La Cellule, 

 vol. XV., 1898. 



