J liscella n eo Us. 1 45 



other countries, and begin to be generally accepted, having been 

 confirmed by such observers as Targioni-Tozzctti, Kessler, Buekton, 

 Horvath, Riley, &c. Nevertheless the facts supporting those 

 theories are still scattered ; for, although it is indisputable that the 

 Phylloxera of the oak, of Boyer de Fonscolombe, passes from Q», ,cti$ 

 coccifera to Quercus pubescens — although Targioni was able to show 

 to his colleagues at Florence Phylloxera florentina passing from 

 Qv> reus ilex to Quercus sessilijlora — although Planchon, Signoret, 

 Cornu, Riley, and twenty more have seen Phylloxera testatrix pas 

 from the leaf-galls to the roots of the vine, the history of the meta- 

 morphoses of the other Aphides has not been much advanced ; and 

 it is a very curious thing that the biological evolution of the genus 

 Phylloxera and of an American species of that genus is much better 

 known to us than that of the Aphides of the poplar or the elm, al- 

 though they occur by thousands of millions ever}' year upon those 

 common trees, defying the unfortunate entomologists who have 

 sought to trace them ever since the days of Reaumur and Linne, 

 and even long before them. 



Various indications had indeed led me to suppose that several of 

 these Aphides must, like Phylloxera, have a phase in their lives 

 when they become radicicolar. Experiments in feeding the Aphides 

 originating from the winged forms issuing from the galls of the 

 Lentiscus upon the roots of grasses, made at Montpellier by SI. Cour- 

 chet and myself, were partially successful. Further, I had found 

 upon these same roots the winged pupiferous form of Aploneura 

 lentisei, which is very easy to recognize, because it is the Pemphigian 

 or gall-aphis that carries its wings flat, like Phylloxera ; but as 

 regards the Aphides of the galls of the poplar and elm nothing has 

 hitherto been discovered. 



The Aphides which form these galls belong to three different 

 genera : 



Pemphigus, represented by about 25 species ; 

 Schizoneura, represented by i) or 10 species ; and 

 Tetraneura, of which we know only 2 species. 



In deciding to trace these last two Aphides, which are called 

 Tetraneura idmi, forming a smooth green gall upon the leaves of the 

 elm, and Tetraneura rubra, Licht., which forms a bright red ru- 

 gose and curly gall, I had more chance* of attaining my object than 

 if I had attacked genera with more numerous species, in which it 

 would have been very difficult for me to refer the subterranean to the 

 corresponding aerial species. Moreover the course was to some extent 

 cleared. At the end of the last century (1770) You Gleichen had 

 carried on day by day for eight years observations upon Tetraneura 

 ulmi during its aerial evolution without discovering any thing ; in 

 resuming these investigations after one hundred years I had dis- 

 covered under the bark of elms the female of this species, with its 

 encysted egg in its body. Prof. Kessler, of Cassel, made a step in 

 advance of this, and found the winged pupifer bringing the sexual 



