5 
Recent Advances in the Study of Heredity. 
happens not rarely that facts apparently inimical to a theory 
become later the strongest supports of that theory if they become 
harmonised with it. 
The parthenogenetic ova in Aphids and Phylloxera do not 
undergo reduction in maturation and it is found that the ova 
destined to become males contain one chromosome less than the 
female ova, the odd chromosome probably being extruded with a 
«■ vWT&tf”' uU 
Fig. 5. 
Fig. 5. Diagram of cytological phenomena manifested in the formation 
of the parthenogenetic ova and gametes in Aphids, a, Sterile spermatozoa. 
b, Fertile spermatozoa, c, Chromosome, probably extruded in polar body. 
mass of protoplasm in a pseudo-heterotype division (see Fig. 5). 
Hence all the cells of the females have one more chromosome than 
the cells of the males, which have five ehromosomes. 
The extra chromosome of the female is therefore undoubtedly 
the equivalent of the x-element described in dioecious forms. 
In the maturation of the oogonia of fertile females ova are 
formed all of which have three chromosomes. The process of 
