422 



iiiid the twenty iii;ii-ked by McAtoe ('05) as common), all ;ire found in the 

 United States and Canada. 1!» reaeli Mexico, 16 Central America, 7 South 

 America east of the Andes, 20 the West Indies, 5 Greenland and 11 are 

 reported from Europe. (See Table No. 2.) 



Of the 24 other water birds listed as rare or occasional from this 

 region, three reach Chili and one Greenland. The range of no individual 

 bird is as great as that of its species, but many of the water birds are 

 gregarious at some season, so that the organisms which they carry would 

 soon be distributed over their entire range. This does not necessarily mean 

 that these organisms would develop over the entire area. 



The following examples show how the ai-ea may be connected with 

 the rest of the globe. Besides the four, indicated in the table as occurring 

 more or less regularly in Europe, others appear accidentally (Headley. 

 "05). The Turnstone (Headley 1. c. ) migrates from Greenland across Eu- 

 rope to Australia. Holboeirs Grebe (Colymbus holboelli Reinh) is dis- 

 tributed over North America, Greenland, Eastern Siberia, south to Japan, 

 thus connectii^g America and Asia. These forms all breed inland so that 

 they are related strictly to the fresh water fauna. The list may, of course, 

 be extended almost indehnitel,^'. Marine birds, such as the albatross have 

 a much wider range but they rarely come inland. 



Birds are the chief agencies in the distribution of Crustacea (cladocera, 

 copepoda), whose eggs are too large to be wind-blown. The reduction in 

 the number of water birds which has taken place in the last half century 

 certainly has reduced the chances of a crustacean reaching a pond at the 

 period suitable to its development. In the larger bodies of water this rela- 

 tion IS not so evident nor so patent because they are much more static. 



Insects migrate very short distances compared with birds. However 

 they do carry organisms from one pond to another in a limited locality. 

 The aquatic beetles and some Ilemiptera are the most efRcieut agencies be- 

 cause the imagoes spend most of their life in the water where algjie and 

 protozoa become attached to them. Occasionally, however, they leave the 

 water, as is attested by the fact that they collect around a light at some 

 distance from their habitat. 



In this pond I have often noted beetles with vorticellfe and other cili- 

 ates attached. The attachment of stalked ciliates to beetles is mentioned 

 by Stein ("54) and otlu>is. .Alignla ("ss) having found a single beetle asso- 

 ciated with algiP in a pool ."lO cm. in diameter near the summit of Biskiden 



