12 Hewitt, Cytological Aspect of Parthenogenesis in Insects. 



unfertilised eggs has been studied chiefly by Blochmann 

 (8) Platner (79) and Henking (44). In Liparis dispar^ 

 and Bombyx niori two polar bodies are formed as in the 

 fertile q^^. In many cases the embryo is unable to 

 complete its development. Nussbaum (72) found that 

 only 2% out of 1,100 unfertilised eggs oS. B. ;;^£>^7 segmented, 

 but they did not hatch out. Henking obtained an 

 unfertilised ovum of Lencoma salicis, but he examined it 

 at too late a stage to observe the formation of the polar 

 nuclei. Tichomiroff (94-99) has caused the partial develop- 

 ment of unfertilised ova of B. mori by mechanical and 

 chemical stimuli. It is difficult to say whether this is a 

 result of artificial parthenogenesis in every case, as the 

 eggs might have had already the power of developing by 

 natural parthenogenesis. 



HEMIPTERA. 



Aphid.e. 



Aphis rosae. Blochmann (8) first investigated the 

 maturation of the parthenogenetic ovum of Aphis. He 

 found that a single polar body was given off. His 

 observations have been confirmed by the more recent work 

 of Stschelkanovzew (91) and Miss Stevens (86). I have 

 recently studied the maturation of the parthenogenetic 

 ovum of this species and my observations confirm those of 

 Miss Stevens. There is a single mitotic division and one 

 polar body is given off from the Qgg. It lies at the peri- 

 phery, but is absorbed later {Fig. 7). The number of 

 chromosomes is 10 and there is no reduction in the single 

 maturation division. They occur in five pairs of different 

 sizes. Stschelkanovzew observed I4 chromosomes in one 

 equatorial plate, but I think he counted chromosomes 



* L. dispar is the destructive ' gipsy moth ' and is also called Ocneria 

 disfar. 



