100 Psyche [June 



genetic reproduction is continuous and uninterrupted, at least 

 among the more common species of tropical aphids. If such a 

 condition does obtain, the most reasonable explanation appears to 

 be that in the tropics conditions are relatively more uniformly- 

 favorable to the aphids, l)oth with respect to the climate and the 

 nutritive factors in the environment. 



Patch (1920), on the other hand, in a very interesting general 

 treatise on the life cycle of aphids, remarks that "in tropical cli- 

 mates experiencing a wet and a dry season gamogenetic [amphigo- 

 nous] eggs are produced to tide over the period of famine"; but 

 unfortnnately she does not cite any specific evidence or authority 

 to support her thesis. It is not improbable, however, that some 

 rare cases of amphigonous forms might occur in those tropical 

 countries where, as she suggests, the year is divided between a wet 

 and a dry season,^ in view of the fact that in the height of the 



^ Such a condition obtains in tlie Philippine Islands, Java, and many other 

 countries of the tropics of both hemispheres. 



hot, dry season, when conditions are less favorable for many living 

 organisms, certain species of insects are known to assume a resting 

 state, presumably corresponding to hibernation in temperate cli- 

 mates. 



In temperate countries, as a rule, reproduction of aphids by par- 

 thenogenesis is continuous during the milder seasons of the year, 

 and amphigonous forms do not appear until the onset of the fall, 

 when the low temperatures begin to affect the insects unfavorably. 

 Exceptions to this generality are determined by the modification 

 of the climate in a given region through the agency of various fac- 

 tors, such, for instance, as the prevailing winds blowing from the 

 ocean and causing the summers to be "more moderate and the 

 winters milder" on the Pacific Coast of the United States than in 

 regions situated at similar latitudes in the interior and on the 

 Eastern Coast.^ The aphids in the former locality are thus sub- 

 jected to comparatively more favorable conditions throughout the 

 year and, consequently, they rarely, if ever, undergo heterogony 

 (Ewing, 1916, and Swain, 1919, p. 8). 



^ R. DeC. Ward. 1918. Climate Considered Especially in Relation to Man, 

 second edition, revised: 44. xvi + 380 pp. G. Putnam's Sons, New York and 

 London. 



