THE WEB OF LIFE 273 



Weiss took the seeds of the gorse, which have a bright 

 orange, fleshy food-body, and placed them on ant-tracks. 

 He found that they were rapidly picked up by the ants, 

 while seeds of various other plants were left alone. The 

 seeds of the broom, which have a food-body like that of the 

 gorse, were treated in the same way. It seems legitimate, 

 then, to conclude that ants assist in the distribution of gorse 

 and broom. 



Mussels and Minnows. The freshwater Mussels (Unio 

 and Anodon) are bound up in the bundle of lif e with fishes, 

 such as minnow and stickleback. The mussel keeps its 

 larvae in a capacious cradle within the outer gill-plate, and 

 does not allow them to escape until a minnow or the like 

 comes into the immediate vicinity. When the crowd of 

 free-swimming bivalve larvae find themselves in the water 

 near the fish they show manifest excitement and move 

 towards it, snapping their valves, which bear minute attach- 

 ing hooks. Fine anchoring threads of a glutinous character 

 are also exuded, and attachment is effected to the minnow's 

 skin. For a considerable time the larvae remain fixed to 

 the fish, pass through a kind of metamorphosis, and eventu- 

 ally fall off into the mud perhaps far from the place where 

 their parents lived. There are many interesting points 

 here the hereditary attraction of the mussel larvae to the 

 fish (in the laboratory they are excited by even a piece of 

 fish), the special adaptations which secure attachment, 

 the metamorphosis, the distribution ; but what we wish to 

 emphasize is the broad fact that two creatures as different 

 as possible the mussel and the minnow have got linked 

 up together. The minnow is quite passive in this linkage, 

 but it is an extremely interesting fact that a continental 

 fish, the bitterling (Rhodeus amarus), should spend part of 



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