THE WORLD OF LIVING ORGANISMS 165 



But every living creature may be worsted in conflict with 

 an adversary, because that adversary has in its organisation 

 other resources at its disposal. 



In tropical countries there are two insects, the centipede 

 and the bird-spider, which occasionally are very troublesome 

 to man by reason of their poison. Once when I was at Dar-es- 

 Salaam, a centipede appeared on our dining-table. I seized 

 a knife and cut it through the middle. The result was that 

 two centipedes ran away in opposite directions. A cut that 

 divides a spider through the middle, finishes it at once. So 

 here the centipede has an advantage. But if one puts 

 both the animals in a glass, one can easily observe that the 

 spider, beginning at the head end of the centipede, slowly 

 devours it. The movement of the centipede, which snaps in 

 every direction with its jaws, does not bother the spider in 

 the least. As soon as the poison- jaw comes near the spider's 

 hairy legs, the leg is lifted up and placed elsewhere. The 

 animal built up of a number of similar segments is quite 

 incapable of attacking its goal direct, and must succumb 

 before the more highly centralised nervous system of its 

 opponent. 



But he who would conclude from such examples that 

 superiority in the struggle is associated with higher differen- 

 tiation, will reconsider his opinion when the life-history of 

 the malaria parasite is put before him. This minute uni- 

 cellular animal has the power not only to adapt itself to the 

 totally different tissue-juices of the mosquito and of man, 

 but is able to find its way about in the anatomy of these two 

 very unlike hosts. 



In this case also, the animal that conquers has some 

 kind of chemical resource, which extends beyond the limits 

 set to the animal that is defeated. 



Without making exact tests, it is impossible to say which 

 animal will have the advantage over another. Sometimes 



