with notice of a new Genus of Diptera. 387 



Phytomyza of Meigcn, of which many of the species in their 

 early stage are known to feed on the parenchyma of leaves. 

 Having traced its states as larva, pupa, and at length a perfect 

 fly, I have been enabled to ascertain the characters of each ; and 

 these, as I am not aware of the field being pre- occupied, I shall 

 proceed to detail ; and although description is often a barren re- 

 gion to travel through, some interesting features of its oeconomy 

 will occur at intervals to lighten the footsteps and reward perse- 

 verance. 



The larva is minute, of a pale glassy green, with the interior 

 darker from the colour of its food ; it gradually tapers away be- 

 hind and is truncate at the tip, but widens towards the front, and 

 is then rather suddenly brought to a point; the segments are 

 regular, distinct, the edges rather elevated, crenulate ; about four 

 or five of the anterior ones are protuberant on the sides, the 

 third being the most prominent ; the first is provided with two 

 bent black oral hooks, which unite interiorly with an apparatus 

 connected with the muscles which put them in play ; [the two fore 

 spiracles have been omitted to be noticed, but they are probably, 

 as in other species, situated behind the head, above ;] the pos- 

 terior end is shaped like the stern of a boat, and is furnished 

 above with two projecting, white spiracular processes, which are 

 barbed like fish-hooks ; the anus is a slit at the tip, between two 

 tubercles. Length f line. It is by means of the hard oral 

 mechanism that it executes its pretty workmanship, whicli it 

 does, while lying like a true miner, on one of its sides, by a 

 rapid and continuous rasping or " raking " of the green matter 

 indispensable to it as food. I have not ascertained when it first 

 commences its proceedings, but on the 13th of August I could 

 only detect a single specimen in the larva state. Usually a leaf 

 is tenanted by only a single occupant ; but there are instances 

 when two have obtained possession, and then the space from 

 which the colour is discharged is proportionally enlarged, and 

 the convolutions are considerably more tortuous. Upon ar- 

 riving at a condition suitable to a change of state, w^hich de^ 

 pends greatly upon the quantity and quality of the food that 

 remains to be supplied, the larva leaves the side of the leaf to 

 which it has hitherto been confined, cuts through the pulpy part 

 of the inferior membrane, till it has reached the lower cuticle, 

 through which it thrusts the tips of its posterior spiracles as well 

 as those of its head, and in this position becomes converted into 

 a small light-coloured pupa, the case being formed of the indu- 

 rated skin of the larva. It has the instinct almost invariably to 

 fix itself alongside of the midrib or one of the secondary fibres ; 

 perhaps being induced to this by the obstacles they present to 

 its progress in mining ; and the case being covered with the thin 



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