THE ADAPTATIONS OF AQUATIC INSECTS. 739 



fourteen segments and the head is provided with hnig slender antenncc. They 

 also possess seta; covered with short hairs. The mandibles are long and 

 curved. The organs of respiration approach closely in structure to the gills of 

 higher animals and consist of leaf-like plates arranged on each side of the body. 

 These, when the living larva is reviewed under a microscope, are seen to move 

 up and down with great rapidity. The larva grows but slowly, some taking 

 two years to complete their metamorphosis. The pupa is active and resembles 

 the larva and traces of rudimentary wings only distinguish it from the latter 

 May fly larva; never come to the surface to breathe and always obtain their 

 oxygen from the water. Aquatic insects may be divided into — 



(1) Those that spend only a portion of their lives in the wa.ter=Culicicla!, 



Odonata, Trichoptera, Ephemeridcc. 



(2) Those that spend nearly all their lives in the water^=^aquatic CoUoptera 



and Rhynchota. 



(3) Thoi^e with quiescent pupEe=C'o/eop/<?nj and 'Irichopttra. 



(4) Those with active piipx=Cidicida' , Rhynchota, Odonata Ephemeridce. 



(5) Those with active pupae differing greatly from adult msect=Culicid(e, 



and other aquatic Diptera. 



(6) Those with active pupae hardly differing from the ]arvEe=OfZowa<a, 



EphemeridcK. 



(7) Those with active pupse hardly differing from adult insects =: 



Rhyncliotar 

 ("8) Those which come to the surface to breathe=CMZ«c/rf«! (larvfB and pupae), 

 Rhynchota (larvae, pupae and adult), Coleoptera (larvEe and adult), 



(9) Those which rarely come to the surface to hvQ2t,ih.=Odonata (larvaa and 



pupae). 



(10) Those which never come to the surface to breathe=Tr2c7to/)/era and 



Ephemeridce (larvee and pupae). 



(11) Those which undergo no metamorphosis and are aquatic all their 



lives = Poduridu;. 

 It is easy to see why the pupae of many aquatic insects are active. Subject 

 to the attacks of many foes few would stand a chance of arriving at maturity 

 had they no means by which to escape. Those insects with quiescent pupas 

 as aquatic beetles and Caddis flies protect themselves by the former pupating 

 in the mud by the side of ponds and the latter in their cases. It was shown 

 in the first part of this paper how the pupa of a gnat breathed and its mode 

 of progression from beneath the water to the surface or vice versa is very 

 curious. At the hinder end of the body is a broad and powerful swimming 

 organ shaped like the telson of a crayfish or lobster. When the pupa wishes 

 to rise or descend this swimming organ is flapped violently towards the head 

 end. By constant flapping the pupa describes a series of somersaults and rises 



* 



It is doubtful if the term pupa is allowable in this order (o/de B. N. H.S.J. , Vol. 

 XVIII, p. 182), but for the sake of convenience I have made use of it here. 

 24 



