312 THE WONDER OF LIFE 



larva which hatches from the egg deposited by the gall- 

 making animal, and there can be little doubt that this is 

 a true interpretation in many cases. But there are other 

 galls which arise apart from insects and mites altogether, 

 namely fungus- made galls, and it is a suspicious fact that 

 there is often a striking structural resemblance between 

 the animal-made gall and the plant-made gall. Therefore, 

 Jules Cotte and others have suggested the theory that many 

 so-called animal-made galls are due to moulds or bacteria 

 or other fungi introduced by the animal. The insect or 

 mite would thus be important not so much in itself, but 

 because it carried a vegetable infection, and, as a matter 

 of fact, many so-called animal galls are demonstrably 

 associated with fungoid growths. Besides the frequent 

 resemblance in structure between animal-made galls and 

 fungus-made galls, there are other notable facts which 

 Cotte utiUzes in his argument. Animals far apart from 

 one another are sometimes able to make very similar galls ; 

 the same animal may produce very diverse galls ; an 

 animal which causes galls at one place or at one season 

 may be inoffensive at another ; there is sometimes a 

 puzzhng disproportion between the dimensions of the gall 

 and the number of its alleged producers ; some galls con- 

 tinue to grow after the animal parasites have disappeared, 

 and others are formed before the egg of the parasites 

 hatches. In any case, we have another illustration of 

 complex interlinking of organism with organism. 



Pearls and Parasites. — ^It is well known that if a 

 foreign body, such as a grain of sand, gets in between the 

 shell of a mollusc and the underlying skin (or mantle) 

 which Unes it and makes it, fine layers of nacre may be 

 deposited around the intrusion and a sort of pearl formed. 



