37 



itself from the pupal skin. Then after a few unsuccessful attempts at 

 aerial navigation (in one observed case three attempts) it flies away to 

 join the insect world. 



The rapidity of insect emergence has often been remarked upon 

 and this species is no exception to the rule. I have, while watching a 

 pupa with thorax exposed above the water, allowed my eyes to wander 

 for a moment, only to find the perfect insect flown, and the hyaline 

 pupal skin floating like a raft upon the water, the thorax spread out on 

 the surface like a boat and the abdomen submerged like a rudder. 



The rapidity of the last metamorphosis is in this case very im- 

 portant for the welfare of the insect, for the emerging fly is liable at 

 any moment to be swamped by the rushing, tumbling stream, splash- 

 ing in and out among the boulders, bearing on its surface the floating 

 pupa skin. 



The time taken to complete the early stages of this Chironomus 

 probably varies very considerably with the temperature. On July the 

 igth, 1907, I placed some freshly hatched larvae in one of my dishes 

 of moving water, and on November i4th, 1907, some of the flies 

 appeared. This gives 118 days rather less than four months for the 

 earlier stages ; but if I had procured eggs in early June, I feel sure 

 they would have completed their metamorphoses in half this time. 



N. B. THIENEMANN has recently divided Chironomus pusio, Meigen, into several species, hut in the 

 absence of specimens it has been impossble to determine which form MR. MUNDY studied. This does 

 not, however, affect the value of his observations. E.E.L. 



