May22, i9i6 Omix geminatella 291 



In the second stage the body is pale, the head becomes brownish, a 

 black blotch begins to appear on the first thoracic segment, legs are still 

 absent, the head capsule is about 0.27 mm. broad, and the caterpillar 

 is about 2.2 mm. long. (Pi. XXXIII, fig. 5, 6.) 



In the third stage the body is at first pale, but darkens with age; 

 the thoracic and abdominal legs appear; the thoracic blotch breaks up 

 into four irregular spots; the head becomes darker and is about 0.35 mm. 

 in breadth, while the caterpillar is about 4.5 mm. in length. (PI. XXXIII, 



fig. 7-) 



In the fourth stage the caterpillar is about 6 mm. long and the head 

 capsule is 0.49 mm. broad; the body takes on an olive-gray color, sharply 

 contrasting with the conspicuous white tubercles; the head becomes 

 darker, and along its hind margin appears a row of four small black 

 spots which parallel the similar row of larger spots on the first thoracic 

 segment. (PI. XXXIII, fig. 8, 9.) 



THE MINE 



While the caterpillar is changing from a pale, flat, footless, micro- 

 scopic caterpillar to a conspicuously marked, cylindrical, active one, 

 its mine also undergoes distinct changes. At first the mine is serpentine 

 in form; but after it is from 4 to 8 mm. in length and is usually curved 

 upon itself, the caterpillar begins to transform it into a blotch mine. 

 (PI. XXXIII, fig. 13.) The blotch mine begins by the third day, and 

 about that time the caterpillar changes to the second stage. At fifst 

 the blotch appears only on the lower side of the leaf. The lower layer 

 of the leaf is separated from the upper by the flat caterpillar, and soon 

 the severed lower layer dies and turns brown. The mine remains in 

 the blotch stage about four or five days, and during that time the cater- 

 pillar changes to the third stage. When complete, the blotch is from 

 I to 2 cm. long and usually occupies all the space between two of the 

 main lateral veins of a leaf. On preparing to produce the tentiform 

 mine, the caterpillar spins silk threads on the floor of the mine, which 

 causes the lower dead layer of the leaf to become folded lengthwise of 

 the mine. These threads, with others spun later under the roof of the 

 mine, cause the upward projection of the mine. Just about this time 

 the caterpillar changes to the fourth stage and begins to feed on the 

 chlorophyll cells, and this in time gives the unspotted effect when a 

 clear net work of veins appears. During the latter part of June it was 

 found that in from a week to 10 days after the young caterpillar begins 

 to feed, the mine is changed from the serpentine through the blotch to 

 the tentiform type. The majority of the feeding and growth occurs in 

 the third and fourth stages, and after the tentiform mine is made it 

 requires from four to seven days to eat out all the chlorophyll cells and 

 give it the completed, unspotted, tentiform appearance. The larval 

 life in the mine is therefore about two weeks. The caterpillar leaves 



