1916] Biology of Aquatic Lepidoptera 167 



III", using an interrogation mark to indicate uncertainty, as. 

 follows: "A transparent caterpillar, essentially like the full- 

 grown ones. The maximum number of gill-filaments is two, and 

 the anterior suprastigmatals and the last three pedals have but 

 one. Length about 4 mm.; head .6 mm." The writer has 

 reared larvae through the early stages from eggs laid by females 

 in the aquaria and observed no indication of an instar between 

 the first and the one described below as the second, the latter 

 corresponding rather closely to the description of Forbes for 

 ''Stage III. (?)". 



A rather surprising change (Fig. 2) takes place at the first 

 ecdysis. The general shape of the larva is not changed but new 

 structures appear. Measurements show the body to be about 

 2.5 mm. long. It is almost transparent, and the color of the 

 material in the digestive tract shows through the body-wall, 

 giving combinations of yellow and green to the general color. 



Head about 0.38 mm. wide, otherwise as in the first instar. 

 Thorax with margins of cervical shield black, remainder trans- 

 lucent ; prothorax with five pairs of well-developed setae ; meso- 

 thorax with one pair lateral, filamentous gills; length of each 

 gill about equal to width of corresponding segment ; metathorax 

 with two lateral, filamentous gills on each side, both of similar 

 length and resembling mesothoracic gills. Legs translucent. 

 Meso- and metathorax devoid of dark color. Abdomen without 

 dark markings ; two lateral gill filaments on each side of all seg- 

 ments except last two, one filament with length about equal to 

 width of corresponding segment, the other about one-fourth 

 shorter; penultimate segment with one lateral, filamentous gill 

 on each side, about as long as width of segment ; ultimate segment 

 devoid of gills. No gills on dorsal surface of body. Last two 

 segments with several pairs of setae, one pair of which is terminal 

 in position, long, and stout. Otherwise similar to first instar. 



The interesting part of the change from the first to the second 

 instar is the initial appearance of the tracheal gills in the latter. 

 In most of the specimens studied, the lateral gills were constant 

 in all respects, but a few showed variation from the typical 

 condition. One specimen showed a small, extra gill on the left 

 side of the ventral surface of the second abdominal segment. 

 Another specimen bore only one gill on the right side of abdom- 

 inal segments II, III, IV, and the left side of abdominal 

 segments II and VII. 



