ANIMAL ECOLOGY OF JOHNSON COUNTY — 35 
have either one of two natural origins, glacial or ox-bow. An 
additional origin permits the existence of artificial ponds made 
by man. While these are not original conditions, the majority 
of them have been established long enough to have acquired most 
of the animal forms of standing water. The ponds of ox-bow 
origin represent simple detached pools of the river and except 
for the fact that the lack of motion of the water reduces the 
oxygen content, the conditions are extremely similar. This is 
rendered more universally true by the fact that almost annually 
the river overflows its banks sufficiently to claim these ponds and 
to restock them with animal life. Several fishes, chiefly carp, 
buffalo, and bullheads, being naturally adapted to life in the 
more sluggish parts of the stream, are able to maintain them- 
selves in these ponds throughout the year. However, as the ox- 
bow becomes reduced by the decomposition of material and the 
establishment of rooted plants, the decreased depth of its water 
will prohibit the maintenance oi the larger animals. The ponds 
of the county are represented on the map (Plate III) by cireles, 
each with a dot in the center. Many of these will be intermittent, 
especially in a dry season such as that of 1896. Even the more 
intermittent of the ponds provide a breeding place for toads, 
frogs, and salamanders, and here their larvae develop. Here, 
too, are normally found numbers of aquatic and semi-aquatic 
gasteropods. 
(2) Swamps. Swamps and bogs represent the half-way 
mark between a body of standing water and dry land. Here the 
vegetation is rich but hydrophytic, and shades into the meso- 
phytie at the margins. Such plants as flags, rushes, and eat- 
tails are common. The soil of the swamp is normally super- 
saturated with moisture throughout the year. Thus a number 
of its forms of life are aquatic or semi-aquatic. Swamps and 
bogs have been indicated upon the county map by stars. They 
are frequently found, where extensive, surrounding a body of 
standing water. In such cases their vegetation provides material 
for the muskrat to build his home. The swampy lands in the 
county form resting places for Wilson’s snipe and the robin 
Snipe on their way to and from the south. Here red-wing black- 
birds nest, and bitterns come daily to take their toll of the tiny 
