E. A. Cockayne 117 



Theoretical explanations of Gynandromorphism. 



Broadly speaking all tho theories of gynanilroniorphisin fall under 

 four heads. 



The first supposes that gynandromorphs are formed from a fusion of 

 two ova or from a binucleate ovum, the second that they are formed by 

 an abnoniialjy dividing single ovum. The third is the Mendelian 

 hypothesis based upon supposed differences in the potency of the sex 

 characters in different races and species, and the fourth is that they are 

 due to abnormal conditions occurring during the development of a 

 normally fertilised ovum. 



Scopoli foreshadowed the first theory by suggesting that his halved 

 gynandromoi-phous Phalaena pint was formed by the fusion of two 

 pupae in one cocoon. 



Dorfmeister's idea is a little less crude. He suggested that two ova 

 in one shell became fused, and then separated each uniting with half 

 the other, and so producing two gynandromorphs. Much more probable 

 is the view put forward by von Ddnhoff in 1860. It was advanced to 

 explain social hymenopterous gynandromorphs and depends on the 

 belief of Dzierzon that all fertilised ova in these insects produce females 

 or workers, and all unfertilised ova produce drones by parthenogenesis. 

 That this is not universally true does not disprove von Donhoff's theory. 

 He suppo.sed that these abnormal insects are produced from an egg 

 with two yolks, ime fertilised and one unfertilised. These fuse and 

 form a single individual, the fertilised part forming part of a worker, 

 and the unfertilised pai't of a drone. Boveri and others also support 

 this view. It might be applied universally on the further supposition 

 that if one nucleus of such an egg is fertilised the other will be stimu- 

 lated to commence cell divisions by the spread of chemical bodies fi-om 

 the fertilised half. In view of Loeb's experiments on artificial partheno- 

 genesis this is not very improbable. 



It is disproved by the existence of perfect halved gynandromorphous 

 hybrids, both sides of which show equal admixture of the characters of 

 both parents. 



Doncaster has recently suggested that a gynandromorph is produced 

 by the fertilisation of each of the nuclei of a binucleate ovum by a 

 separate spermatozoon. He has proved the existence of these binucleate 

 ova and has actually proved the conjugation of a separate spermatozoon 

 with each, and srcn the resultant mitoses. The theory is a fascinatingly 



