THE MARGUERITE FLY. 39 



like a papilla of the much larger second segment, and contains, ventrally, 

 the mouth opening; segments thi-ee and four are comparativelj^ short; 

 the five terminal segments are distinctly longer than the five segments 

 immecUately anterior to them. Two contiguous subcylindrical caudal 

 spiracles, dark terminally, project backward from the dorsal portion of 

 the apical end of the last segment. These spiracles are connected by 

 sinews and branched, longitudinal, dorso-lateral, tracheal trunks, one on 

 each side of the body, with the two contiguous cephahc spiracles situated 

 dorsaUy on the posterior portion of the second segment, each caudal 

 spiracle being connected with the cephahc spiracle on its own side. The 

 anal opening is located at the posterior end of the terminal segment, on 

 the ventral aspect. At the anterior end is seen the dark-colored chitinous 

 and forked oral appendage or rasping organ, conspicuous for its dark 

 color. 



The rasping organ or rake is composed of two similar halves lying side 

 by side. They are joined at some points in their course, and the interval 

 between them at other points is so small that it is difficult to make them 

 out at those points as distinct pieces. Each haK consists of a short, stout 

 anterior piece or head, the anterior margin of which is modified into strong 

 teeth, and of a more slender and elongate posteriorly forked framework 

 to which the toothed head is attached. The upper of the two posterior 

 prongs is somewhat arched and is longer than the straight lower one. 

 The two halves are joined for a short distance in the vicinitj^ of the heads 

 and at the posterior portions of the lower prongs. The heads are but 

 slightly separated. The whole works as a unit. 



In the mine the larva lies on one side, moving along by bodily or mus- 

 cular contractions aided very hkely by its rasping organ, — which can be 

 seen with the aid of a lens, swinging quite rapidly in a dorso-ventral 

 plane, — with which it can grasp and attach itself to the leaf tissue. Taken 

 out of the mine, or uncovered within the mine by rupturing the overlying 

 epidermis, it is practically helpless. It seems unable to pierce the epidermis 

 of the leaf and start a new mine, nor does it know how to continue feeding 

 in the opened mine. Feeding is, as a rule, attempted, but the attempts 

 are feeble. Thus exposed, it remains active for some time, but its help- 

 lessness in this new environment is plainly apparent; its various motions 

 bespeak but a helpless despair. The bulk of its energy soon spent, its 

 activities gradually lessen and finally cease, death resulting in a few hours 

 — the time depending upon the conditions to which it is exposed — from 

 a loss of bodily moistiire. In water it continues to hve for a much longer 

 period — one lived for slightly over twenty-four hours. 



As will be recalled, the eggs are as a rule placed from the lower surface, 

 immediately above the epidermis. The larvae on hatching, however, do 

 not remain feeding on the spongy parenchyn:ia. With a few exceptions 

 they soon make their way to the palisade parenchyma immediately below 

 the epidermis of the upper surface, where they continue for the remainder 

 of their larval existence, going down again, as a rule, only when the supply 



