182 THE THEORY OF EVOLUTION 



cord of the sheep. The malaria Parasites (some 

 Plasmodium species) would have had, in that case, 

 from the beginning the positive task of causing 

 fever and death to man, 1 since only to that end are 

 they constructed. Only in the red corpuscles of the 

 blood of man or in the intestine of the mosquitoes 

 (some Anopheles species) can the various reproductive 

 stages be carried through. 



Have there been from the commencement beings 

 whose existence is necessarily dependent upon a constant 

 exchange of relations between men and mosquitoes ? 3 

 If the man be not there, then the purely vegetative 

 increase cannot happen and therewith the first condition 

 for further development falls to the ground. If there 

 be no mosquitoes then the sexual generation cannot 

 take place, and the play is at an end. The malaria 

 Parasites are thus physiologically formed for this mode 

 of life i.e. they have the need of so existing and the 

 necessary equipment to attain their object ; therefore 

 the spores introduced into the blood have a pointed 

 form, to enable them to bore into the blood corpuscles. 



(c) Had the parasitical mode of existence been 

 present from the beginning, particularly to its present 

 extent and in its extreme development, then there 



1 According to investigation so far the Malaria Plasmodes occur only 

 in man and as a phase of Schizogonia (= increase by formation of several 

 individuals from one by fission). F. Doflein : Die Protozoen als Parasiten 

 und Kranlcheitserreger, Jena, 1901, p. 145. 



2 Ibid. p. 130. We have to do with Parasites which, ' in the exchange 

 of hosts between two organisms, live in man and a member of the Fly 

 family ' ; also, p. 147 : ' Another mode of transfer than through the 

 mosquito cannot be according to our present knowledge.' 



