(32 [ August, 



SO, indeed, than was M. le Professeur Balbiani, who had on former 

 occasions declared such a migration quite opposed to entomological 

 and botanical laws. 



Moreover, as only one species of Femphigus is known on the elm 

 tree, viz. : the PempJiigus pallidiis, Haliday (sub. Eriosomci), I fancied 

 it was now a very easy job to gather galls of that insect wlien tbe 

 emigration takes place, to put the emigrant winged-lice on roots of 

 maize, and to notice how they throve. 



Under a bell glass I placed some good clean garden earth, in 

 which I had planted some grains of Indian corn, and I thought, at the 

 same time, I could try also to put besides the Pemphigus galls the other 

 four galls of the elm tree.* There is a sixth gall-louse on elm, the 

 CoIopJia compressa, but it occurs only on Uhnus effusa, and never on 

 JJlmus campestris in which the others are abundant. Well, to my 

 great disappointment, not one of the young Pemphigus touched the 

 maize-roots ; they were all dead and dried up, in a few days. But, to 

 my still greater astonishment, the young of Tetraneura uhni, the most 

 common of all the elm gall lice, fixed themselves immediately on the 

 tender rootlets of the plant, and went on sucking and growing so 

 satisfactorily, that, in ten days, they had acquired nearly double their 

 previous size, and were covered with the usual white secretion, which 

 we generally see on these insects. 



Immediately the idea occurred to me that M. Horvath finding a 

 root-louse on the Indian corn, had jumped to the conclusion that it 

 could be no other than the Pemphigus zece-mdidis, and had never 

 thought that it might be a Tetraneura. 



Indeed, the di:fference between the two genera is a very trifling 

 one : Tetraneura has but one cubital nervure in the under- wings, while 

 Pemphigus has two, and no under-ground species of Tetraneura is 

 known up to this time. 



Hence, I wrote to Prof. Horvath : — " Please, dear friend, send me 

 at once what you call PempJiigus zece-mdidis." By return of post I 

 had the insect ; I put it under the microscope, and saw at once it was 

 a Tetraneura, and the very Tetraneura ulmi upon which Baron von 

 Grleichen began his well-known observations, in Niiremberg, in 1770, 

 and of which the full biology has also been discovered only in 1882, in 

 Budapest ; so now we know exactly : 



1st.- — ^That the " Tetraneura uhni " comes out of eggs deposited 

 in the crevices of the trunks of the elm tree, in the beginning of 

 May, and forms a gall on the leaf. It is the Pseudogyna fundatrix. 



* Viz. : SckUoneura ulmi and lanuginosa, Tetraneura ulw.i and rubra. 



