38 Hewitt, Cytological Aspect of Parthenogenesis in Insects. 



EXPLANATION OF PLATES. 



^. Egg nucleus, /i. Outer half of first polar nucleus, /'i. Inner 

 half of first polar nucleus. p2. Second polar nucleus. 

 Pb. Polar body. S. Syntelosome (= p'\ + p2). 



Plate I. 



I. Formation of polar nuclei in parthenogenetic egg oi Nematus 



ribesii (diagrammatic after Doncaster). 



First polar spindle. 



First polar spindle dividing into the two polar spindles 



of the second polar mitosis. 

 Second polar mitosis. 

 Egg nucleus {e) and three polar nuclei. 

 Fig. 5. Fusion of two inner polar nuclei to form the syntelo- 

 some. 

 Fig. 6. Resolution of syntelosome into 16 chromosomes. 



2. Aphis rosae. 

 Figs 7. Two mature parthenogenetic ova of Aphis rosae in their 

 follicles. The single polar body of the upper ovum 

 lying at the periphery ; the polar body of the lower 

 ovum has been absorbed: x 1500 (drawn with 

 camera lucida). 



