22 Cutler, Parthenogenesis in Animals 



thing else." The first objection to the hypothesis is the inherit- 

 ance of certain characters in the Lepidoptera and Birds where it 

 is necessary to assume that the order (of things is feversed. As 

 I have already mentioned , however, there is evidence to show 

 that in these two groups there is an odd element in the female. 

 This is a very remarkable confirmation of the theory of the 

 connection between chromosomes and sex, and as Doncaster 

 remarks, " It Can hardly be coincidence that the spermatozoa 

 should be dimorphic in respect of a chromosome in the forms in 

 which sex limited inheritance by the male takes place, and the 

 eggs dimorphic in the same way in thoBe in which sex limited 

 transmission is by the female. 



How then does this theory accord with the facts of partheno- 

 genesis ? In the Ants, Bees and Wasps a male is produced from 

 eggs which have undergone reduction in the chromosome number. 

 This is also the case with Hydatina senta, and probably so in 

 Litomastix. Thus the female has the diploid, the male the hap- 

 loid chromosome number. If, as Nachsteim suggests, in the bee, two 

 of the chromosomes are sex chromosomes, in the female one of 

 them is extruded at maturation and the iegg will develop into a 

 male. As all the spermatozoa of the male contains the sex 

 chromosomes females must result from fertilisation. Whether 

 the sex chromosomes are present or not: in the female does not 

 affect the theory, for the important point is that the male con- 

 tains half the number of chromosomes found in the female. 



The observations of Jack and Wheeler, showing that in rare 

 cases workers may produce females from the unfertilised eggs, 

 cannot be discussed until the cytology olf these eggs is investi- 

 gated. Three possibilities are open to account for this variation. 



(A.) There may be two maturations, but both equational, as in 

 the Saw-fly, Pcecilosoma luteolum. 



(B.) There may be but one maturation division which is not 

 reductive. 



(jC.) There may be non-disjunction of sex chromosomes, if these 

 exist. 

 This phenomenon of non-disjunction was suggested by Bridges 

 as the result of Work on Drosophila. He found that on rare 

 occasions the sex chromosomes of the egg stick together at the 

 maturation divisions, and are both extruded with the polar body 

 or both remain in the female pronucleus. If, in the case of the 

 bee, both chromosomes remained in the female pronucleus the 

 resulting insect would be a female. 



Rhoditis and Poecilosoma. — In both these insects females are 

 almost invariably produced from the unfertilised eggs, and the 

 maturation divisions are in both cases equational, which is in 



