PHFLL0XERID2B. 63 



following valuable summary. M. Lichtenstein is 

 accomplished both as a biologist and a linguist, and the 

 reader will note not only his concentration of the sub- 

 ject within a small space, but also will appreciate the 

 clear English he employs, of which language he has 

 made himself a proficient. I here heartily thank 

 him for the material help he has given me in the 

 preparation of this Monograph. 



Summary on the Genus Phylloxera. A Letter ad- 

 dressed to the Author by M. Jules Lichtenstein 



La Lironde, Montpellier ; 



September 10th, 1882. 



My dear Sir, 



You ask me to give you a note on the genus 

 Phylloxera, which I have now had under particular 

 observation ever since 1868. I am sorry to say I 

 am not able wholly to explain in a satisfactory way 

 the very curious metamorphoses of these Proteus- 

 like insects, which seem to defy the endeavours 

 of naturalists to group them by sharp and rigid 

 characters. 



As you have already mentioned in your work on 

 ' British Aphides ' my ideas about the biological evolu- 

 tion of plant-lice in general, and gall-lice in particular, 

 I can spare your readers a good deal of explanation ; 

 and begin with a short affirmation of a theory, which 

 is now about ten years old, and which all my sub- 

 sequent observations lead me to confirm. 



With reference to the hypothetical frame I have 

 fancied of Aphis evolution, I will shortly indicate what 

 I know surely to be true, and what I suppose to be so, 

 but cannot as yet bring to rigid proof. First of all I 

 am of opinion that the evolution of plant-lice is 

 entirely different from the common metamorphosis of 

 other insects ; and, as Baron von Gleichen, De Geer, 

 and Gotze said before me, I think the only way of 



