194 



der 1914 p. 46). We have seen that variation in habits has most probably taken 

 place also with C. pipiens and T. annulata. 



I suppose that the whole question with regard to variation in bloodsucking 

 habits in mosquitoes must be regarded from the same point of view, viz. that 

 species with a wide area of distribution are not forced to live their life in quite 

 the same manner as those of the northern and southern limits of their area. Fur- 

 ther that when some species are carried out of their normal distribution-area and 

 are suddenly forced to live in another area, their biological range of variation is so 

 great that they are able (o begin life again under other conditions than those to 

 which they were originally adapted, and in the course of a short time conform 

 their whole organism to the new claims. Finally when a new factor appears in 

 their old distribution area and disturbs the once-sanctioned order of environment, 

 the organisms are to a certain degree able to accomodate themselves to the new 

 factor and this latter again is able, to a degree which almost seems incredible, to 

 alter the biology of the said species. 



The peculiar fact that many hymenoptera of the order Fossoria use different 

 forage for their young ones and use the paralytica] instinct here and upon Corse 

 in different ways (Benwex a. o.); the variation in instinct from fruiteaters to blood- 

 suckers of the Nestor parrots of New Zealand; the variation in instinct of the Au- 

 stralian Dingos, the variation in instinct in the biology of different species of beetles 

 (Haltica, Anthrenus) which, suddenly transferred from the old world to the new or 

 vice versa, grow to be noxious animals of great economic significance in their 

 new home, whereas in their original home they are quite harmless animals; the 

 alterations in the biology of the swallows which, from being originally inhabitants 

 of rocks and mountains nowadays owing to the building of castles, church steeples 

 etc. build their nests upon or in our houses over vast areas of distribution; the 

 variation in the life of Turdus merula in the last generation of man, are all ex- 

 amples of the same above-named common rules. With regard to the Anophelines 

 the above named changes in the agriculture of our own and adjacent countries was 

 the new factor which in our latitudes altered the biology of this Anophelin species. 



When I consider the malaria curves in the time from about 1830 to 1900 and 

 see how rapidly the curves fall and remember that malaria has disappeared from 

 our country in the course of only one or two generations of man, I find that the 

 variations in the habits of A. maculipennis have taken place not as an ''evolution 

 lente" but very suddenly and with an almost incredible rapidity. From Roubaud's 

 investigations we are entitled to suppose that the variation in habits has at all 

 events also affected the animal morphologically; if this holds good for more 

 than the size we do not know; a more thorough investigation of the mouthparts, 

 especially the number and size of the sawteeth on the maxilla; which are in fact 

 subject to variation, would most probably give interesting results. I think that it 

 must be admitted that in the variation in the habits of .4. maculipennis there really 



