214 CALIFORNIA ACADEMY OF SCIENCES. [Proc. ^d Ser. 



watch the process carefully, and he describes it in his Manual 

 (p. 435) as follows: — 



" Each midge on emerging forced its way out through a 

 transverse rent between the thorax and abdomen. It then 

 worked its body out slowly, and in spite of the swift current 

 held it vertical. The water covering the patch of pupge 

 varied from one-fourth to one-half inch in depth. In the 

 shallower parts the adult had no trouble in working its way 

 to the surface, still clinging to the pupa-skin by its very 

 long hind legs. While still anchored by its legs, the midge 

 rests on the surface of the water for one or two seconds 

 and unfolds its wings; then freeing its legs it takes flight. 

 The adults emerging from the deeper water were swept 

 away by the current before they had a chance to take 

 wing. The time required for a midge to work its way out 

 of the pupa-skin varied from three to five minutes." 



As is obvious, the whole process of emergence and escape 

 into free air must be a quick one. Usually with insects it 

 takes some time for the proper expansion of the wings, 

 which are, in the pupa, neither wider nor longer than the 

 pupal wing-cases, but attain their full size only after with- 

 drawal from these cases. But in the Blepharocerid there 

 is no time for that; the slender legs cannot hold long against 

 the beating of the swift water, and so the remarkable con- 

 dition of a full development and expansion of the wings in 

 the pupa obtains in this family. The fully developed wings 

 lie in the pupal case folded both longitudinally and trans- 

 versely, and only need to unfold to be ready to carry the 

 fly into the safe air. It is this folding which produces the 

 secondary veining of the wings characteristic of the family, 

 this veining being simply the persisting creases and lines of 

 the folding (PL XXI, figs. 7 and 8). 



The writer has often watched the emergence of adults, 

 and has been struck by the great loss (apparently) of life 

 in the process. So many are swept away by the swift water 

 before the wings can be unfolded or before the legs can be 

 loosened from the pupal sheath, that it seems no wonder 

 that the family is a disappearing one. It is a case of the 



