392 



THE BIOLOGY OF INSECTS 



of the chromosomes." We have noted in a previous chapter 

 (p. 139) that the production of sexual or virgin forms 



Fig. 82. — Sections through Potato-leaves pierced by Hemiptera. 

 a, piercing stylets (/)) of Leaf- hopper (Eupteryx) penetrating tissues, 

 s, sheath of hardened saliva, t, tracheid ; b, puncture by Eupteryx at 

 lower surface, saliva surrounding track {tr) of piercers ; c, piercers of 

 Mealy-bug (Dactylopius) with branching tracks in phloem shown by 

 saliva. X 600. After K. M, Smith {A?7n. Appl. Biol, xiii, 1926). 



follows from alternative modes of nuclear behaviour, and 

 it is possible that the germinal modifications for such changes 



