420 Wisconsin Academy of Sciences^ Arts, and Letters. 
ance. This strip is rarely more than nine meters wide, and in 
Lake Mendota is easily recognized, even where separated from 
the breaker line by extensive shoals. 
Physiologically, it is a region of great molar activity, and, 
with its more or less shifting bottom, presents certain definite 
ecological aspects. The animal (or plant) that desires to live 
there must be able to meet (a) great molar action of wave and 
undertow, (b) a partly shifting bottom as a result of molar 
action, (c) extremes of temperature, and motion, (d) prolonged 
periods of hunger,—in general, sudden changes to which other 
parts of the lake, except the breaker line, are not subject. 
In horizontal section, the shore line may be classified into 
rocky shores, stony or gravel shores, and sandy shores. The 
lake shallows will be treated as part of the vegetation area. 
Each of the shores is more or less distinct in its conditions and 
associations, and will be treated separately. 
A. The Rocky Shores .—In Lake Mendota these occupy about 
a fifth of the lake circumference. The physical aspect is that 
of large boulders, shattered rocks,—in general an appearance of 
roughness. The width of the rock shore is usually from 8 to 10 
meters, its depth often being continuous to 6 or more meters; 
for the purposes of ecological association the depth to 1 meter 
alone will be considered. The slope of the rock shore is usually 
considerable, and the surf line is practically always continuous 
with it, generally marking the lower edge. 
In its physiological aspects the rock shore indicates the great¬ 
est exposure to molar agents found in the lake. The heavy 
waves, the surf, the strong undertow and its accompanying 
drift, the swift changes from quiet to turmoil, present condi¬ 
tions which relatively few animals are equipped to meet. 
The only plant found is Cladophora, a filamentous alga, the 
plumes of which are conspicuous at all times of the year. An 
elaborate system of clinging rhizoids, and great pliancy of the 
plumes enable it to meet the conditions of wave action. Since 
it needs the sunlight for food manufacture it is never found on 
the underside of rocks. 
The animals in turn, except the visitors, are practically con¬ 
fined tOi the underside of rocks (see table 8, p. 471). They 
must, therefore, not only meet the action of the general molar 
agents, but must protect themselves from the undertow and the 
shifting rubble. To meet wave action, the prime response is to 
