VOL. XXII. 3 PHILOSOPHICAL TRANSACTIONS. 515 



some of the blossoms of a quince tree, that had a great many of those black 

 flies upon them, and put them into a glass tube, in order to make my obser- 

 vations of them. I observed that those flies would not live above two days, 

 and that some of them had laid a great number of longish eggs. The reason 

 why they live no longer, I thought might be the want of food ; I was there- 

 fore resolved to observe what the flies did, as they sat upon the leaves of [\\e 

 plum trees, and found that they had insinuated themselves into the curled 

 leaves of the trees. 



The leaves of these plums, and of other fruit trees, were covered with a 

 great number of small creatures, that are frequently found on the leaves of 

 currant and cherry-trees, which creatures we here call lice,* some of them 

 being green, and others which are sometimes less, and of another shape, black- 

 ish, and both sorts in time become flies. 



On the 20th of May, I plucked four little leaves off a plum-tree, upon which 

 were 36 of those black flies, besides some hundreds of those little creatures we 

 call lice, and amongst them several little ones that were newly come Out of 

 their mother's belly ; all these with the leaves I shut up in a glass tube. Of 

 the 36 flies, most of them were females, and had their eggs in them, except 

 one that had laid hers against the sides of the tube. Amongst these flies I 

 found two sorts, with this difference, only that the hoorn vliesen, wherein their 

 eyes are placed, were in some of them four times as large as in others. 



As the flies did not live above two days in the last closed tube, I went again 

 on the 25th of May into two distinct gardens, because I could find but one 

 fly in the first garden, where there had been so many before ; and in the other, 

 where there had been many thousands both of flies and lice, I could with great 

 care get but nine. These were all females, and had their eggs in them ; from 

 whence I more strongly concluded, that the black flies did the trees no harm ; 

 for if they had laid their eggs on the trees, and all their eggs'*had produced 

 living insects, there would not, I am positive, one leaf, or any fruit have re- 

 mained on the trees. After these last flies had remained two days, and as 

 many nights, shut up in the glass tube, there were but three left alive. And 

 the next day these were dead also. 



Upon the occasion of taking these flies, and the great number of lice that 

 S^t upon the leaves, of which I have given a draught, in my printed letter of 

 the 10th of July 1695, where I also said that these creatures bring forth their 

 young without copulation ; I shall send you a draught of them, as if I had 



* These insects belong to the Linnsan genus /ipA«, and exhibit the wonderful phenomenon of a 

 continued impregnation througii several successive generations. 



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