THE WEB OF LIFE 269 



istic adhesive cells which grapple with small animals pass- 

 ing by. 



Another good instance of linkage, which is not obvious 

 at first glance, is the connexion between fishes and malaria. 

 But it is not a hard riddle to read. The parasite which 

 causes malaria is disseminated by the mosquito, and the 

 larval mosquitoes are devoured by many fishes. Captain 

 R. B. Seymour Sewell and B. L. Chaudhuri have described 

 eleven Indian fishes which are of proved value as mosquito 

 destroyers. They conclude that ' fishes may be a very 

 important agent ia regulating and diminishing the degree 

 of malarial infection in any given district '. It has also 

 been suggested that the reason why the Barbadoes are 

 remarkably free from malaria, is that the mosquito larvae 

 are devoured in large numbers by a small fish, popularly 

 known as ' milHons', which is very abimdant in all the 

 streams and pools. 



The practical lesson to Man is the obvious one that he 

 cannot be too careful lest he disturb the balance of things, 

 by extermination on the one hand, or by transplantation 

 on the other. We have elsewhere referred to important 

 instances, such as the introduction of rabbits into Australia 

 and of house-sparrows into the United States. We may 

 refer again to the story of the rats of Jamaica. Rats 

 brought by ships became a plague in Jamaica. To cope 

 with them the mongoose {Herpestes griseus) was imported, 

 and it made short work both of the Old World rats and the 

 Jamaican cane-rats. But when these were gone, the 

 appetite of the mongoose remained, and the poultry and 

 various ground birds began to suffer. Useful insect-eating 

 lizards were also eaten, and another cloud rose on the sky — 

 there was a multiplication of injurious insects and ticks, 



