VOL. LXXIII.] PHILOSOPHICAL TRANSACTIONS. 3S7 



and in 7 or 8 days more, the entire plants, except the stronger fibres, were eaten 

 up. A border under the hedge was regularly spared till the body of the inclo- 

 sure was finished ; but this done, the border was soon stripped, and the gateway, 

 and even the roads have been seen covered with caterpillars travelling in quest of 

 a fresh supply of turnips ; for the grasses, and indeed every plant, except the 

 turnip and the charlock (sinapis arvensis) they entirely neglect, and even die at 

 their roots, without attempting to feed on them. This destruction has not been 

 confined within a few miles of the eastern coast, but has reached, more or less 

 into the very centre of the county. The mischief however in the western parts 

 of Norfolk, and even on the north coast, has been less general ; bat it is thought 

 that one half of the turnips in the county have been cut off by this voracious 

 animal. 



The following is Mr. M.'s description of the insect in its different states. The 

 wings of the fly are 4 ; the antennas clubbed, and about -l of the length of the 

 body, each being composed of Q joints, namely, 2 next the head, above which 

 2 there is a joint somewhat longer than the rest, and above this 6 more joints, 

 similar to the 2 below. Near the point of the tail of the female tiiere is a black 

 speck, outwardly fringed with hair ; but which, opening longitudinally, appears 

 to be the end of a case, containing a delicate point or sting, about -JL of an inch 

 in length, which on a cursory view appears to be a simple lanceolated instru- 

 ment, with a strong line passing down the middle, and serrated at its edges ; 

 but, on a closer inspection, and by agitating it strongly with the point of a 

 needle, it separates into 3 one-edged instruments, hangerdike as to their gene- 

 ral form, with a spiral line or wrinkle winding from the point to the base, making 

 ]0 or 12 revolutions, which line, passing over their edges, gives them some ap- 

 pearance of being serrated. 



By the help of these instruments probably the female deposits her eggs in the 

 edges of the turnipdeaf, or sometimes perhaps in the nerves or ribs on the under 

 surface of the leaf. Mr. M. having put some , fresh turnip-leaves into a glass 

 containing several of the male and female flies, he perceived, by means of a 

 simple magnifier, that one of the females, after examining attentively the edge 

 of the leaf, and finding a part which appeared to have been bitten, unsheathed 

 her instruments, insinuated them into the edge of the leaf, and having forced 

 them asunder so as to open a pipe or channel between them, placed her pubes 

 (the situation of which from repeated and almost incessant copulations he had 

 been able to ascertain precisely, and to the lower part of which these instru- 

 ments seem to be fixed) to the orifice, and having remained a few seconds in that 

 posture, deliberately drew out the instruments (which the transparency of the 

 leaf held against a strong light afforded -him an opportunity of seeing very 

 plainly) and proceeded to search for another convenient place for her purpose. 



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