282 Transactions. 



be gently transferred from one leaf to another ; it is. however, extremely 

 rapid oi flight. Almost invariably on the withdrawal of the ovipositor 

 from the leaf the fly will immediaetly turn and eagerly lap the exuding 

 sap. Whether this is merely to satisfy her own immediate wants or is in 

 some war connected with the welfare of the egg is from data in hand a 

 debatable point. Before continuing the process of laying the ovipositor 

 and body generally are subjected to a thorough cleansing ; all extraneous 

 matter is removed. The egg-laying capacity of any individual probably 

 reaches about 200 ova. 



Often cavities that have been carefully probed will be left without an 

 egg. This is hard to explain; probably at the moment the ovum was not 

 ripe within the ovaries. Pockets might be begun in tough portions of 

 the leaves, but in such places they are hardly ever completed, and no eggs 

 are deposited in them. The time taken in probing a cavity and depositing 

 the egg rarely exceeds a minute. During the proceedings the back legs 

 are at times violently stamped upon the leaf. Occasionally leaves are 

 found crowded with these pockets, but in such cases only a few of them 

 will contain eggs. 



The ovum is cylindrical, pearly- white, glossy, ends rounded : the shell 

 is very delicate, and devoid of any kind of sculpturing. The micropylar (?) 

 end is slightly broader than its nadir. Length. 0-32 mm. : greatest 

 diameter, 0-15 mm. 



The larva (Plate III. fig. 2) hatches on the sixth day after the laying 

 of the egg. It at once begins burrowing in the soft inner substance of 

 the leaf, keeping close against the upper cuticle. Burrowing now goes 

 on unceasingly for the next nine days. The mine often assumes fantastic 

 forms, sometimes crossing and recrossing itself many times ; as the larva 

 grows, the mine, of course, gradually widens and becomes very conspicuous 

 as a white figure upon the green leaf. A thin line of minute frass granules 

 occupies the middle portion of the floor of all mines. During the last three 

 days the larva pushes ahead with great rapidity, as a glance at Plate II 

 will show. The following figures are from another mine that was kept 

 under careful observation : Distance pierced by larva during the first day 

 of its larval existence. \ in. ; second day. \ in. in all ; third day, \ in. ; 

 fourth, f in. ; fifth, 1| in. : sixth. 2 in. : seventh. 3 in. ; eighth, 5 in. : ninth, 

 7f in. — total length of mine. 



The larva (Plate III, fig. 2) is a minute cylindrical grub, broadest near 

 the head ; white in colour, inclining to light green on account of the 

 assimilated food within the intestines and the transparency of the skin. 

 The head is to a certain extent retractile. The following measurements 

 are from a full-grown larva : Length, 3-0 mm. ; greatest breadth, 0-9 mm. 

 Posteriorly there are two minute black respiratory processes ; a second 

 pair, situated anteriorly on the head, are slightly longer, and white. 



The mouth-armature of the adult larva differs sufficiently, on account 

 of the mode of feeding, from that of other dipterous larvae to warrant a 

 detailed description. It consists of two horizontal plates connected by 

 a slender cross-bar ; these are the cephalo-pharyngeal apophyses. Each 

 consists of three processes — an anterior (fig. 14, a), narrowing towards the 

 great hooks ; a posterior (p). broadening slightly towards the extremity : 

 and a mid-lateral process (ml), which is spinular, and directed posteriorly. 

 The two great hooks, placed side by side, present three processes — -a large 

 anterior curved sickle-like process, a like but smaller mid process, and 

 a broad blunt triangular heel. The whole cephalo-pharynx is deeply 



