CuAr. XII. FRESn-WATER PRODUCTIONS. 353 



vanced a;^c ihoy would voluntarily drop olT. These just- 

 hatched moUusks, thoui^h aquatic in their nature, survived on 

 the duck's feet, in damp air, from twelve to twenty hours ; and 

 in this lenp^tli of time a duck or heron mij^ht (ly at least six or 

 seven hundred miles, and, if blown across the sea to an oceanic 

 island or to. any other distant point, would be sure to alight on 

 a pool or rivulet. Sir Charles Lyell informs me that a Dj'tiscus 

 has been cau2;ht with an Ancylus (a fresh-water shell like a 

 limpet) firmly adhering- to it ; and a Avater-beetle of the same 

 family, a Colymbetes, once flew on board the " Beagle," when 

 forty-five miles distant from the nearest land : how much 

 farther it might have been blown with a favoring gale no one 

 can tell. 



With respect to plants, it has long been known what 

 enormous ranges many fresh-water, and even marsh-species, 

 have, both over continents and to the most remote oceanic 

 isFands, This is strikingly shown, as remarked by Alph. de 

 Candolle, in large groups of terrestrial plants, ^vluc]l have only 

 a very few aquatic members ; for these latter seem immediate- 

 ly to acquire, as if in consequence, a very wide range. I 

 think favorable means of dispersal explain this fact. I have be- 

 fore mentioned that earth occasionally, though rarely, adheres 

 in some quantity to the feet and beaks of birds. Wading- 

 birds, which frequent the muddy edges of ponds, if suddenly 

 flushed, would be the most likely to have muddy feet. Birds 

 of this order, I can show, arc the greatest wanderers, and are 

 occasionally found on the most remote and barren islands in 

 the open ocean ; they would not be likely to alight on the sur- 

 face of the sea, so that the dirt would not be washed off their 

 feet ; and, when making land, they would be sure to fly to their 

 natural fresh-water haunts. I do not believe that botanists 

 an; aware how charged the mud of ponds is with seeds : I 

 have tried several little experiments, l)ut will here give only 

 the most striking case : I took in February three table-spoon- 

 fuls of mud from three different points, beneath water, on the 

 edge of a little pond: this mud when dry weighed only GJ 

 ounces ; I kcjit it covered up in my study for six months, pull- 

 ing up and CHjunting each plant as it grew ; the plants were 

 f)f many kinds, and were altogether 537 in number; and yet 

 the viscid mud was all contiiined in a breakfast cup ! Consid- 

 ering these facts, I think it would be an inexplic;d)l(> circum- 

 stance if water-birds did not transport the seeds of the same 

 fivsh-water plants to unstocked ponds and streams, situated at 



