Entomology of the Illinois River. 191 



15 larvae were still present, though iu diminishd num- 

 bers, but careful search failed to reveal a single pupa 

 or imago. In the breeding-cages the larvae spent much 

 of their time in the deeper water, their tubes extended 

 but not reaching the surface, and at other times were 

 hidden near the surface, the tubes extended, their tips 

 making a minute hollow in the surface film, but instantly 

 withdrawn if the cage or its contents were disturbed. 



Towards the end of March, the larger larvEein the breed- 

 ing cage began to show a swelling and hghter color of 

 the thoracic segments, and on March 29 an examination 

 of the cage was made which revealed four pupae. 

 The loose skin of a larva about to pupate was removed, 

 revealing the soft white pupa. [See Fig. 18.] The left 

 respiratory tube was rudimentary and crooked. The 

 other was coiled between the larval and pupal skins, 

 forming first a double spiral on the right side, then 

 passing around beneath to the left side, where it formed 

 a similar spiral, then crossing the dorsum to the right 

 side again, and making a turn or two there, among the 

 first coils, finally ending at the middle of the under side, 

 having extended one and a half times around the seg- 

 ment. In making this extensive growth it seems to 

 have crowded out and dwarfed its fellow of the left 

 side. The tube rapidly straightens out after puyjation, 

 and soon becomes quite straight and bristle-like. The 

 pupae [Fig. 19] are able to move a little bj' efforts at 

 crawling and by side-to-side strokes of the posterior 

 extremity. One was isolated and rested quietly in a 

 vertical position, the end of the tube just above the sur- 

 face of the water. April 6 this produced a fine female im- 

 ago, and another emerged a few hours later iu the stock 

 cage, each leaving its empty skin floating at the surface. 

 Next day a male appeared in the cage, and a number 

 of pupae were found to be present. One of the examples 

 which emerged had had the greater part of its breathing 

 tube accidentally broken off several days before. Pupae 



