1916] Biology of Aquatic Lepidoptera 177 



dependent, to some extent at least, upon the degree of develop- 

 ment of the quiescent stage, the length increasing as the time 

 of emergence of the adult approaches. All of the appendages of 

 the head and thorax become more and more apparent and it is 

 often possible to pick out the female pupae by the uniform dark 

 slaty gray appearance of the front wings. The leg cases become 

 increasingly distinct and acquire an external segmentation 

 corresponding to that of the enclosed leg. 



The abdomen is widest at its junction with the thorax and 

 tapers gradually caudad. Except at the extreme posterior end 

 of the body, the intersegmental grooves are broad and well- 

 defined. The second, third, and fourth abdominal segments 

 bear each a pair of large, lateral, conspicuous spiracles, all of 

 nearly uniform size, and borne on fleshy, conical tubercles. The 

 slit-like opening is transverse in position and surrounded by an 

 almost circular, dark orange, chitinized peritreme. Separated 

 from the peritreme by a narrow space and at a slightly lower 

 level is a fine, brown, concentric line. The various structural 

 elements of these spiracles vary in size in the dijfferent specimens 

 and to a limited extent in the same specimen. The average 

 dimensions of the peritreme are about 0.232 x 0.264 mm., the 

 average length of the slit-like opening is approximately 0.14 

 mm., and the average diameter of the outer ring is about 0.28 

 mm. Vestigial spiracles occur on abdominal segments V-VII 

 but are so inconspicuous that close examination under mag- 

 nification is usually required to locate them. The ventral sur- 

 face of the tip of the abdomen bears a number of short, longi- 

 tudinal carinae, arranged in two groups. The intersegmental 

 grooves in this region are obscure and careful examination is 

 required to determine the segmental position of these groups 

 of carinae. The anterior group occurs on the eighth abdominal 

 segment and usually consists of a single, median carina or a 

 pair of similar carinae, one on either side of the median Hne. 

 The second group of carinae occurs near the anterior margin of 

 the ninth abdominal segment and consists of a single, median 

 carina separating the components of a pair of similar carinae. 

 Sometimes a second pair of lateral carinae are also present. The 

 crests of the carinae in both groups are brownish in color while 

 the sides have the same color as the adjacent parts of the 

 abdomen. 



