4 ROBERTS, On t7vo cases of Parallelism in the Aphidce 



the poplar to Ranunculus at Midsummer. On Ranunculus 

 two generations are produced, the second of which, as I 

 understand Tullgren's description (5) to mean, are the 

 sexuparae. These migrate back to the poplar and there 

 produce the sexuales ( 6* , ? ), from which the fertilised 

 ova, producing the stem-mothers of the next year, are 

 derived. 



But Mordwilko has observed (and his observation is 

 confirmed by Tullgren) that when the sexuparae leave the 

 Ranunculus, wingless individuals remain on that plant, 

 and that the species is still to be found there during the 

 winter. Tullgren's observation of this parallel race relates 

 to the early part of June, a time when the stem-mother of 

 the ordinary life-cycle is on the poplar. He then found 

 wingless insects on Ranunculus, and by the end of the 

 month these had flown away, though where they had 

 flown to we do not know. Possibly it may have been to 

 other Ranunculus plants, in which case they would cor- 

 respond to the generation known as " exsules alatae " in 

 certain species of Chermes. 



My own observations fully confirm the main facts of 

 the life cycle given by Tullgren, as the following epitome 

 will show : — 



Winged $ ? (migrants) — most had already flown — 

 poplar. 25.vii.i3. 



Apterous $ ? and larvae. Ranuncuhis. 15.vii.i4. 



Winged 9. $ (sexuparae) and larval sexuales — poplar. 

 6.IX.14 — io.x.14. 



Apterous £ $ and larvae. Ranunculus. 9.x. 14. 



These last were sent to me by my friend, Mr. T. A. 

 Coward, from Bovvdon, and it will be seen that these 

 wingless $ $ coincide in point of time with the winged 

 sexuparae, which migrated to the poplar. Doubtless the 

 larvae would have continued to live on the Ranunculus 



