10 Hewitt, Cytological Aspect of Parthenogenesis in Insects. 



Cynipid.e. 



Rhodites rosae. Thelyotoky and deuterotoky both 

 occur in the gall-flies. Henking (44) has studied the 

 maturation of the unfertilised ovum of Rhodites rosae. In 

 this insect the males are rare, but they are occasionally 

 found. Henking found that in the nucleus of the ovarian 

 egg there were only nine chromosomes, the somatic number 

 being 18. The nucleus undergoes two divisions; three 

 polar nuclei and the female pronucleus are formed in this 

 manner, each containing nine chromosomes. In the 

 cleavage nucleus, however, 1 8 chromosomes were observed. 

 The second polar nucleus and inner half of the first polar 

 nucleus fuse, the outer half of the first polar nucleus going 

 to the periphery. Later the outer half of the first polar 

 nucleus wanders inwards, and fuses with the syntelosome. 

 This takes place about the same time as the female pro- 

 nucleus begins to divide. As Henking did not examine 

 any later stages he throws no light on the fate of the 

 ' polar' nucleus. 



In the maturation divisions of Rhodites there is no 

 reduction. The doubling of the chromosomes in the 

 female pronucleus before undergoing division is also 

 interesting. Henking considers that there was a pairing 

 of chromosomes before the first maturation division — the 

 pairs being resolved at the beginning of the cleavage 

 divisions. 



DIPTERA. 

 Paedogenesis occurs in this order of insects in some 

 species of Miastor, a genus of the Cecidomyidae and in 

 Chironomus. 



Miastor. Metschnikoff (63) studied the development 

 of the unfertilised ovum of this insect. Although he was 

 unable at that time to investigate the minute nuclear 



