THE ADAPTATIONS OF AQUATIC INSECTS. 741 



of 11 j^nat pupa* long stift hairs [Jioject, Thcsu no duiilit serve to give a 

 1,'reater impetus to the springing motion when swimming referred to above. 

 A European species of aquatic 1 1 ijmenoplerous insect Palynema nufans swims 

 by means of its wings which are fringed with a row of fine hairs. - 



(4) The hairs in the respiratory trumpets of a gnat pupa are seen when 

 examined under a microscope to be extremely fine and close set, and from two 

 to three hairs spring from each root. 



The long hair-like filaments on tiic adult May flies (^Ephemera) besides 

 doul)tIess serving as organs of perception {vide Part I) are of use in at least 

 two other ways. The flight of these insects is for the most part a sustained 

 rising and falling. When rising the filaments are kept close together, but on 

 the descent these are spread out in exactly the same manner that the 

 feathera of a bird's tail are spread iii flight. Might not these act like a 

 parachute and break the insect's fall (they never apjiear to move the wings at 

 all in descent) somewhat ? I found that a captured May fly deprived of its 

 filaments did not fly at all well, but of course it might have been injured 

 in other ways besides. Each filament of a May fly is divided into a number 

 of squares and each square is covered with minute thick set hairs resembling 

 those found in the respiratory organs of a gnat pupa. Doubtless they serve 

 the same function that is to protect the female from undue moisture during 

 the period of egg deposition. Swammerdam found ' that a species of May fly 

 Polymitarcijs virgo — which had fallen on a napkin spread over his knees that — 

 " they could only rise into the air with the help of tlieir long tail filaments 

 which gave a momentary support to the body." 



(5) Hairs that act as organs of preception, see my remarks on Ephemera in 

 the first part of this paper. 



Regarding the economic uses of aquatic insects I find that the vast clouds 

 of mosquitoes and May flies seen over the African lakes are compressed into 

 cakes for food by the Africans and dried in the sun. (Theobald.) 



A few hints regarding the preparation of insects for the microscoi)e taken 

 from Messrs. Cross and Cole's ''Modern Microscopy" may be of use. 



Insects should be killed with chloroform. They are then to be placed in 

 methylated spirit, in which they may remain until required for mounting. 



To prepare a whole insect for mounting with pressure in Canada Balsam, 



(1) Transfer from methylated spirit to water, and let it soak for three or 

 four hours to remove spirit. 



(2) Place in liquor potassaj* 10 per cent, of caustic potash in distilled 

 water until soft. Some specimens will only require a few hours in the potash, 

 others need days, and some even weeks to soften. In all cases they must be 



1 The term mjmph. here is often employed, 



2 Lubbock Z,JH» Trans, Vol. xxiv, p. K!') (l!*i;::). 



3 Biblia Naturae. 



* Any chemist can supply the ingredients mentioned here. 



