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it immediately darts towards the bottom". The statements are in accordance with 

 the common opinion and contain also what can be termed half of the truth, but 

 the thesis gives no expression to the other half. 



It must be remembered that the mosquitoes pass from larva; to pupae imme- 

 diately below the surface, live their whole life as pupa; in the same locality, and 

 even pass the last ecdysis from pupae to imagines in the very same place. As far 

 as I know this is not the case with any other insects but the mosquitoes. 



If we keep mosquito pupa; in aquaria, it can be shown that voluntarily they 

 never leave the point of support which they have once acquired, that is to say: if 

 the acquarium is never moved and if it always stands in the shade. I have in my 

 aquaria reared imagines from pupa; which most probably have never made a single 

 somersault movement. I suppose that even in Nature it may happen that many pupa* 

 moult without having made more than very few movements. 



If we observe a pond where almost the whole swarm rests as pupa in the 

 surface, we see, in fact, that the single individual moves very little and that there 

 are long pauses when we see no movement at all. Only two alterations in the 

 surrounding medium: different light reflexes and disturbing agencies of the water 

 layers; are able to make the pupa release their hold and alter their place below the 

 surface. The light reflexes are especially brought about by sunbeams which suddenly 

 strike the surface of the pond from a cloudy sky. As highly phototactic the pupa 

 often arrange themselves after a line, corresponding with the edges of the sunbeams 

 in relation to the shadow. The pupa are directed by their highly developed com- 

 pound eyes which do undoubtedly function, a remarkable feature by which the 

 mosquito pupa diverge from most insect pupa. 



The disturbing agencies are mainly heavy raindrops, the circles of which pro- 

 duce a curious influence upon the swarm, and enemies of the pupa; of these they 

 have mainly three kinds. The Hydrometridcv pounce upon the pupa from above 

 and insert their rostrum in the cephalothorax. It is very remarkable to observe how 

 numerously the Hydrometridiv appear upon ponds where most of the swarms have 

 been altered into pupa; how suddenly they appear, and how suddenly they dis- 

 appear again as soon as the pupa have been hatched. From below the pupa are 

 preyed upon by Notonectidce and the larva of various Dytiscidce, more especially by those 

 belonging to the genus Rhantus which are always found in great numbers in mos- 

 quito ponds; it seems as if their whole existence is dependent on mosquito larva 

 and pupa, their whole development coinciding with the development of the mos- 

 quito larva; this coincidence is adjusted to such a degree that the Dytiscid larva 

 and mosquito larva follow each other with regard to the single ecdysis; it is a 

 very curious picture to see the Dytiscid larva, black with white venters, on a morning 

 when the total number of mosquitoes in an almost dry pond have suddenly 

 left the water, cross the water-masses like sharks in search of that prey which 

 they were deprived of almost at once, and which even on the foregoing day was 



