4(> PROCEEDINGS ENTOMOLOGICAL SOCIETY 



in so far as it was possible, we bred the progeny from alate and 

 apterous mothers in all cases. This necessitated the handling 

 of a large number of experiments, there being at some periods 

 as many as two hundred and fifty running simultaneously. It 

 was found to be impracticable, under these circumstances, to 

 select only the first and last born to represent each generation, 

 as appears to be the usual custom. Consequently, we allowed 

 two sisters, or cousins, as the case might be, in one generation, 

 to produce the next and reared from a few to as many as sixty 

 insects to maturity in every case, selecting our mothers for the 

 next generation when they had reached the adult stage. This 

 method has one great advantage over the other, in that it pro- 

 vides an abundance of bred material for further study. 



In these experiments we obtained an adult form quite distinct 

 from any of the normal adults of the species. This adult was an 

 intermediate between the alate and apterous vivipara, or rather 

 it is an alato with a tendency to degenerate to the apterous 

 condition. 



In the fourth or last nymphal instar, aphids which will become 

 alate are strongly differentiated from the earlier stages and from 

 the corresponding stage of the apterous form (fig. m). The 

 thoracic segments are more clearly differentiated from each other 

 and from the abdomen. The prothorax is narrow with nearly 

 straight margins, while the proximal angles of the mesothorax 

 form two prominent, rounded shoulders. The entire body is 

 more narrow and elongated. The meso- and metathorax bear 

 large wing pads. The color also varies in this form, the head 

 and thorax being orange yellow with a rosy bloom, while in apter- 

 ous insects they are yellow-green, concolorous with the abdomen. 

 The wing pads are dark gray in color. Because of its resemblance 

 to that form in the metabola, we follow the general custom and 

 call this stage a pupa. It should be stated, in this connection, 

 that the possession of wing pads also pertains to the third nymphal 

 instar of this form, but in this case they are very small and their 

 presence is not accompanied by any of the other special char- 

 acters noted. 



The fourth nymphal instar of this intermediate is apparently 

 identical with the pupa of the normal alate aphid. The measure- 

 ments of the antennal segments, the cornicles and the posterior 

 tibiae are the same for both. In one case of five pupal moults 

 mounted on a single slide, four being from insects which became 

 normal alates and one from an intermediate, we were unable to 

 separate the moults from each other. In handling the insects 

 we usually transferred the "potential" alates to new plants, in 

 the pupal stage. In no case of the selection and transfer of these 



