Chap. XII.] MEANS OF DISPEESAL. 147 



excrement; and several of these seeds retained the 

 power of germination. Certain seeds, however, were 

 always killed by this process. 



Locusts are sometimes blown to great distances from 

 the land ; I myself caught one 370 miles from the coast 

 of Africa, and have heard of others caught at greater dis- 

 tances. The Eev. E. T. Lowe informed Sir C. Lyell that 

 in November 1844 swarms of locusts visited the island 

 of Madeira. They were in countless numbers, as thick 

 as the flakes of snow in the heaviest snowstorm, and 

 extended upwards as far as could be seen with a tele- 

 scope. During two or three days they slowly careered 

 round and round in an immense ellipse, at least five or 

 six miles in diameter, and at night alighted on the 

 taller trees, which were completely coated with them. 

 They then disappeared over the sea, as suddenly as they 

 had appeared, and have not since visited the island. 

 Now, in parts of Natal it is believed by some farmers, 

 though on insufficient evidence, that injurious seeds are 

 introduced into their grass-land in the dung left by the 

 great flights of locusts which often visit that country. In 

 consequence of this belief Mr. Weale sent me in a letter a 

 small packet of the dried pellets, out of which I extracted 

 under the microscope several seeds, and raised from 

 them seven grass plants, belonging to two species, of 

 two genera. Hence a swarm of locusts, such as that 

 which visited Madeira, might readily be the means of 

 introducing several kinds of plants into an island lying 

 far from the mainland. 



Although the beaks and feet of birds are generally 

 clean, earth sometimes adheres to them : in one case I 

 removed sixty-one grains, and in another case twenty-two 

 grains of dry argillaceous earth from the foot of a part- 



