6 Royal N. Chapman 



The eggs assume a whitish appearance about ten minutes after oviposi- 

 tion, and gradually turn black, until, after forty-eight hours, they are a 

 shiny black, as previously stated. Owing to the crescentic shape of the 

 developing embryo, the eggs may appear to be slightly larger on one side 

 than on the other. Under ordinary conditions they hatch in about ten 

 days. 



Emergence of the larva 



The larva emerges from the egg by eating its way thru the side adher- 

 ing to the leaf, and passes directly into the leaf tissue without exposing 

 itself to the exterior. The fact that the egg is firmly attached to the leaf 

 makes it possible for the larva to obtain leverage as it eats thru the leaf 

 epidermis. The longitudinal veins of the leaf are just far enough apart 

 to allow the flattened head and thorax of the larva to pass between them 

 and permit it to enter the parenchyma, where it is surrounded by an 

 abundant food supply. 



The course taken by the larva as it first begins to mine its way about 

 in the leaf seems to vary. It begins eating at once, forming a blotch 

 mine which gives the leaf a blistered appearance. Some larvae begin to 

 mine toward the tip of the leaf, while others mine on the side toward the 

 base of the leaf. In either case the burrow assumes an area of three or 

 four square millimeters in about twenty-four hours, and then the larva 

 proceeds to mine toward the opposite end of the leaf. Ordinarily this 

 alternating between one end of the mine and the other seems to con- 

 tinue until the larva has reached maturity. 



An egg that was kept under constant observation hatched on June 13, 

 and the larva made a mine, two square millimeters in extent, toward 

 the base of the leaf the first day. By July 7 the mine measured 4 by 6 

 millimeters, the major part of which was toward the tip of the leaf. On 

 July 17 the mine measured 4 by 55 millimeters, 35 millimeters of the 

 length being toward the tip of the leaf. In three more days the burrow 

 was complete, measuring 98 millimeters in length, and extending 35 milli- 

 meters toward the tip of the leaf and 63 millimeters toward the base. 



The completed burrows were found to vary in length from 62 to 170 

 millimeters, and they usually extended from the midrib to the margin of 

 the leaf, often causing the leaf to become rolled. A few leaves were 

 found in which the larva had crossed the midrib and continued its mine 

 on the other side. Others were found in which as many as four larvae, 

 working in the same leaf, had united their mines into one, and all the 

 larvae had matured successfully. 



In feeding, the larva devours all of the tissue between the two layers of 

 the leaf epidermis. Its body, including the prothorax, remains stationary, 

 while its head moves from side to side until all the tissue within reach has 

 been eaten. Then the prothorax is crowded forward, forcing the two 

 layers of epidermis apart. From the new position, the process of eating 

 all the tissue within reach is repeated. In holding the prothorax in 

 place and in moving it forward to a new position, the small appendages 

 of this part of the body seem to be used very much like ordinary pro- 

 thoracic legs. 



At the end of each instar the larva evidently returns to the central part 

 of the mine to molt, for it is here that all of the castings, and eventually 



