238 A NATURALIST IN HIMALAYA 



of birds and therefore be carried more securely than 

 univalves ? Birds have frequently been shot with 

 cockles clincrinof to their bills. Bivalves have been 

 found with their shells firmly closed on the legs or 

 antennae of water-beetles, or grasping the limbs of 

 water-scorpions or the larvae of dragon-flies and other 

 inhabitants of fresh-water pools. There would seem 

 to be little doubt that the habit which bivalves possess 

 of lying with their shells apart and closing tightly 

 on objects introduced between them would make them 

 more liable to transportation than univalves, and give 

 them a greater opportunity of being the first arrivals 

 at a newly formed and distant pool. This appeared 

 to me the probable explanation of why this isolated 

 pool should have been stocked only with bivalves. 



All creatures are dependent one on the other in the 

 well-balanced scheme of life. One species is essential 

 to another for food, to another for shelter, to another 

 for the rearing of its young. Destroy any one species, 

 and some other will surely suffer Even the life of 

 the molluscs is interwoven with that of the higher 

 animals in that they use the migration of the birds and 

 the agricultural devices of man as an unconscious 

 mode of transport to scatter them over the surface 

 of the earth. 



