10 



Aquatic ILitt 



ous tiny, boat-like masses appear on the 

 surface of the water, each mass consist- 

 ing of 200 to 400 eggs. These soon hatch, 

 and as the larvae breathe at the surface, 

 they may be collected with a small net, 

 one "scoop" of which often yields the 

 equivalent of an egg-cup full of wrig- 

 glers. Some species deposit their eggs 

 singly; others lay in damp places, where 

 water will later collect and the tggs, re- 

 main dry for some time. 



The larvae of different sorts of mos- 

 quitoes sometimes exhibit considerable 

 variation. The accompanying illustra- 

 tions, from photographs by the author, 

 show a quite common type. Apart from 

 its capacity as a fish food, this wriggler 

 is well worth careful examination. It is 

 protected with numerous tufts of hair, 

 and some of the hairs are branched or 

 feathered. Unlike the condition in the 

 adult, the two brown eyes are of simple 

 construction. There are two crescent- 

 shaped brushes of hair round the mouth 

 in place of the biting mandibles of other 

 insects. If the larva is viewed alive 

 through a magnifying glass, these brushes 

 will be seen in rapid motion. Their 

 function is to create a current whereby 

 small animalcules or particles of vege- 

 table matter are carried to the mouth 

 organs. Predaceous and cannibal larvae 

 have stronger hairs in the feeding 

 brushes, these then being used to seize 

 the prey. 



Respiration is effected through a 

 breathing tube at the posterior end of the 

 body. This is the longer of the caudal 

 tubes in the illustrations, but it varies in 

 length in the different species. One au- 

 thority observed that examples with a 

 short tube are mostly found in temporary 

 pools, whilst those with a long one occur 

 in permanent waters. The orifice is only 

 opened when the insect comes to the sur- 

 face to breathe. It is closed at will with 

 five or six little leaves, an ingenious 



mechanism by means of which water is 

 prevented from finding its way into the 

 air passages. When closed the tube is 

 sharp and pointed, and is thus easily 

 pushed through the surface film, which 

 would otherwise offer considerable re- 

 sistance to so tiny a creature. Once the 

 film is pierced, the flaps open out in the 

 form of a cup, which floats and enables 

 the larva to remain suspended head 

 downward. 



In a certain group some members of 

 which convey malaria, the larva has 

 respiratory openings, but no external 

 breathing tube, and clings to the surface 

 film by means of broad hairs. 



Air is conveyed to the various parts 

 through numerous tracheae, or air pipes, 

 which ramify through the body in all 

 directions ; some of these tracheae may be 

 seen in the photo-micrograph of the head. 

 The shorter and thicker tube is the last 

 abdominal segment, and the exterior ter- 

 mination of the digestive canal. The 

 vent is protected by long hairs, and has 

 a pair of thin, finlike tracheal gills on 

 each side. 



The larval form is maintained for a 

 fortnight or thereabouts, the time some- 

 times being longer, owing to cold weather 

 or paucity of food. During this period 

 the skin is shed three times ; at the fourth 

 moult the pupal stage is assumed. The 

 insect does not now at all resemble its 

 previous state; it is still active and swim- 

 ming is accomplished by strong jerks of 

 the abdomen, at the termination of which 

 two paddles are attached. Digestive ap- 

 paratus is absent and the organs of res- 

 piration are greatly changed. The caudal 

 tube is lost in casting the skin, and the 

 pupa breathes through two little funnels 

 situated on the back, near the head. 

 When not in motion it floats at the sur- 

 face and the openings of these funnels 

 are held just above the water. The in- 

 sect, which, as development proceeds, can 



