1920] Patch: Aphids and Coccids 159' 



apple less generous for their needs, and their ancient enemies 

 have smelled their blood and come to slaughter under the roof 

 of wax. And then the migrant, true to the instincts of the 

 clan in the hour of need, quietly escapes and bears the torch of 

 life home to the elm. This voyage of the fall migrant seems 

 inexplicable. It is neither her hunger nor that of her unborn 

 brood that urges her forth for neither she nor her dwarfed, 

 beakless progeny feed on the elm. It is not a quest for a mate, 

 for she, like her maternal ancestors for five generations, gives 

 parthenogenetic birth to her young. But, whatever the cause, 

 once and once only in seven generations the fall migration takes 



III. HoRMAPHiDiNi. Life Cycle of Honnaphis hamamelidis. 

 (Three generations). 



I. Fundatrix apterous viviparous female; hatching from overwinter- 



ing egg; causing and developing within the witch 

 hazel gall; reproducing by parthenogenesis. 



II. Sexuparae alatae Alate viviparous females; developing within the witch 



hazel gall; dispersing to witch hazel leaves; reproduc- 

 ing by parthenogenesis. 



III. Sexuales dwarf, apterous male and oviparous female; both with 



beaks developing on witch hazel leaves; female laying 

 several fertilized eggs. 



I. Eggs overwintering on witch hazel. 



(For the vicinity of New York, adapted in part from T. H. Morgan and A. F. Shull) 



place from secondary to primary host, as once and once only 

 in seven generations the reverse migration of the spring occurs. 



Any one such life cycle as that just indicated, though rep- 

 resentative, must be specific rather than comprehensive. 



An inter-food-plant migration would seem to have become 

 typical of the Aphididae, for it is met in ten* or more widely 

 distributed tribes; although in many instances the migration 

 is restricted to fresh plants of the same species, a modification 

 that obscures its significance. 



That the environment is influential in the production of 

 the winged forms, thus giving the mechanism for migration, is 



*Aphidini, Myzini, Macrosiphini, Anoeciini, Mindarini, Schizoneurini, Pro- 

 ciphilini, Pemphigini, Hormaphidini, Pterocommini. 



