3 ! 4 Problems of Organic Adaptation 



can be reached only by a particular route and by certain spe- 

 cies of insects, and the pollen is so located in the flower that 

 masses of it will become attached to the proboscis or other 

 portions of the insect, and these masses will then be depos- 

 ited upon other flowers of this species visited by the insect. 

 Both flowers and insects are benefited by this adaptive rela- 

 tionship. The yucca moth collects pollen from one flower of 

 the yucca, flies to another flower and lays her eggs among the 

 ovules, and then places pollen upon the stigma, without 

 which fertilizing act the ovules would not develop. As the 

 larvae of the moth develop, they eat a part of the ovules but 

 leave a part, so that seed is produced, and thus both species 

 are perpetuated. This act is performed but once in the life 

 of a moth, so that there is no opportunity of learning by ex- 

 perience or imitation. It is a principle in such mutual depen- 

 dence that each member must conserve the other, and even 

 in parasitism the parasite must not usually destroy the host 

 else it will at the same time destroy itself. 



Extraordinary cases of adaptation are found in the pe- 

 culiar life histories of certain parasites, which must pass 

 through one or more larval stages in intermediate hosts 

 before they reach the adult stage in the final host. Consider, 

 for example, the almost infernal ingenuity shown in the life 

 history of the malarial organism, which adapts it to life in 

 the mosquito and in man and to its transfer from one to the 

 other; or the adaptations shown in the life history of the 

 liver-fluke, which passes through four different larval stages 

 in one or two intermediate hosts before reaching its final 

 host; or the life histories of the tapeworm or hookworm or 

 trichina, which are wonderfully adapted to securing the sur- 

 vival, multiplication, and distribution of these parasites. 

 Perhaps nothing in nature exceeds in complexity and nicety 

 of adaptation the life histories of such parasites. 



