422 
and the twenty marked by McAtee (05) as common), all are found in the 
United States and Canada. 19 reach 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 area may be connected with 
the rest of the globe. Besides the four, indicated in the table as occurring 
more or less regularly in Europe, cthers appear accidentally (Headley, 
95). The Turnstone (Headley |. c.) migrates from Greenland across Eu- 
rope to Australia. Holbcell’s Grebe (Colymbus holboelli Reinh) is dis- 
tributed over North America, Greenland, Eastern Siberia, south to Japan, 
thus connectivg Americn 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 slmost indefinitely. Marine birds, such as the albatross have 
a much wider range but they rarely come inland. 
3irds 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 pateut 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 Tlemiptera are the most efficient agencies be- 
cause the imagoes spend most of their life in the water where algre and 
protozoa become attached to them. Occasionally, however, they leave the 
witer, 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 vorticellzee and other cili- 
ates attached. The attachment of stalked ciliates to beetles is mentioned 
by Stein (54) and others. Migula (SS) having found a single beetle asso- 
ciated with alge in a pool 80 cm. in diameter near the summit of Biskiden 
