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

 further exceptional case has been recorded by 1'erez, 1 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 2 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, 3 showing 

 that sperm nuclei are not found in drone eggs whereas they are 

 commonly met with in worker eggs, supply an important confirmation 

 of Dxierzon'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. 4 



Among the Tenthredinida' or sawm'es 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. 5 



In the parthenogenetic Rotifer, Hy<l<itin<i, 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, "M6moire sur la Ponte de PAbeille reine et la Thcorie de 

 Dzier/on," .1 /'//"/<.< <l \at., vol. v., 1*7--. 



2 Sanson, "Note sur la Pluth&iogen&e <-h<-/. Irs Abcillcs," .|/////.-x </.<x 

 Science* \<it., vol. v., 1878. 



3 Petrunke\\ itx-h, ' hie EtiaktaffifftikBrper mid ihr S.-hicksal im Ix-fruchteten 

 und unbefruchteten Bienenei," Z<>l. ./>!/,,-/>., vol. xiv., !!)()!. ''has S.-hicksal 

 der RichtungskorpiT im Drohnenei," /."<>!. ./>r/,,-/>., vol. xvii., I'.HIL'. 



4 Wheeler, "Tin- Origin of Female and \Vork-r AnU from tin- Kggs of 

 Parthenogenetic Workers," .SVvVnr, vol. xviii., 1!K)3. 



5 DoncastiT, "On the Maturation of tin- I'nfn t ilix-d KLT.U' ami the Fate of 

 the Polar P-odirs in the '/'</////, ,///,;,/,/. " (Jim/-. Jon,-. .!////. >'<///<-, vol. \li\., I! KM;. 



Maupas, "Sur la Multiplication ft la Kf<-ondation <Ic 1'Hydatina scuta. 

 ('. II. ili' l'.\i'<nl. '/.< >'/., vol. radL, ISIHI. --Snr la K.Voiidat ion ,|,. lllydatina 

 senta," C. H. <>> /".!'</. <!,* >'.-/., vol. cxi., IH!X>. "Sur la I )ctcriuinisinV de la 

 Sexualiti' chcx. Hydatiua /.!. i X /., \ol. cxiii., 1891. Lenssen, 



Contribution a 1'Ktude du I >< -\ c|o|iii'iiiiMit. dr., (lit-/, niydatina, /." r,// ,//,-, 

 vol. xv., 1898. 



