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spread tracheal gills and peculiar thorns upon the dorsal side of the abdomen. 

 Then the skin bursts and in the course of a second the subimago stands upon the 

 surface, whereupon it takes wing and reaches the coast. A few hours later the 

 subimago undergoes a new ecdysis, and the aerial wings appear, hyaline and 

 without thorns. 



I am inclined to suppose that even many naturalists are unacquainted with 

 the fact that the Trichoptera pupae, after a resting stage in the closed and fastened 

 larva cages on the bottom of the water, are free-swimming organisms for a short 

 time of their life; as such, without using air in any way, they actively ascend to 

 the surface; the swimming apparatus is the second pair of legs, furnished with a 

 brush of long swimming hairs; at the very moment the surface is reached, 

 the tracheal gills, the lateral line of long hairs round the abdomen are thrown out 

 upon the surface; partly by means of these organs, partly by peculiar thorns and 

 plates on the dorsal side of the abdomen, the pupa is now fastened to the surface 

 and supported by the surface film. In this position the cuticula bursts in the middle 

 line over the thorax; its lateral parts are, just as in many Ephemeridce and Culi- 

 cidce pupae, spread out upon the surface; a swimming bridge, a point of support is 

 thus gained; by means of reception of air the imago pushes itself out of the 

 skin, using the broad outspread thoracic plate as a support for the legs; some of 

 these pupae (Leptoceridce, f. i. Mystacides a. o.) ascend vertically from the bottom at 

 such an almost incredible speed that they only use their legs for three or four 

 strokes; the moment they arrive at the surface, the skin bursts with an audible 

 sound, and the imago is almost hurled out of the skin into the air, where it 

 immediately takes to its wings. In these species the free-living pupa stage is almost 

 incredibly short, the time from the moment it leaves the pupa-case till it is, so to 

 speak, thrown into the air as a flying insect, may be counted in seconds. But even 

 in these few seconds of life a swimming apparatus is necessary, and just and only 

 for that purpose and, as far as we can see, for these three or four strokes of the 

 middle legs, these legs are formed as swimming legs with broad tibia and brushes 

 of long soft hairs. 



The Chironomidce from the bottom of our deepest lakes act almost in the 

 same manner; there is only this difference that the pupae do not reach the sur- 

 face by active motions, but ascend passively and perpendicularly to the surface by 

 means of air formed between the pupa- and imago skins; here they occupy a hori- 

 zontal position; the thorax bursts and the mosquito creeps out and stands for a 

 moment upon the outfolded pupal thoracic skin. Lying in a boat on calm sum- 

 mer evenings I have heard a sound of bursting bubbles round the boat, and 

 convinced myself that it originated from the bursting pupal skins when the air 

 escaped. 



To this same group of water insects which complete their last ecdysis upon the 

 surface of the water belong also the Culicidce; from the Ephemeridce Trichoptera and 



