IO4 GEORGE O. SHINJI. 



case with the chestnut aphis (Myzocalis castanet), the ulmus aphis 

 (M. ulmi), the oak aphis (M. quercus, etc.), the birch aphis 

 (Euceraphis betula), the linden aphis (Eucallipterous tilicB) and 

 others. These species do not grow on any other host plant 

 except their specific ones, nor are they easily reared on cuttings, 

 or even on young potted seedlings. Although the writer failed 

 to produce apterous forms of these Chaitophorini, the develop- 

 ment of wings in these species is no doubt due to the nature of the 

 host and also due to the feeding habits of the aphids, for all the 

 young are apterous. 



The aphids infesting willows, wheat, clematis, pea, radish and 

 other plants were occasionally experimented with, several sub- 

 stances being used, as in other experiments. The development 

 of the wings in these aphids could also be controlled. 



IV. THE PERIOD DURING WHICH THE DEVELOPMENT OF THE 

 WINGS MAY BE CONTROLLED. 



Professor Clarke has suggested that the fate of the wing-buds 

 may probably be determined near the end of the first molt, 

 while Professor Woodworth thinks it can be predicted as early as 

 one day after birth. The fact that one hundred per cent, of 

 winged aphids can be produced on a twig charged with mag- 

 nesium salts as late as three days after planting the twig, led 

 Neiils to carry on a series of experiments along this line. By 

 transplanting young aphids from a twig charged with distilled 

 water to one charged with magnesium salts, he found that rose 

 aphids could be made to produce wings if they were subjected to 

 the magnesium solution within three days after birth. I have 

 partly repeated his experiments and also extended them to other 

 species with the following results: 



It is seen from the above results that the period during which 

 the development of the wing-buds can be controlled varies with 

 the species. I have also observed in the course of my experi- 

 ments that the aphids infesting the German ivy (Senecio sp.) 

 develop the wing-buds within sixty hours after their birth. 



