432 Wisconsin Academy of Sciences, Arts, and Letters. 
so varied in their diet, others so restricted? Why should cer¬ 
tain caddisworms be algophagous, while others feed on any plant 
and will readily eat animal food ? 
It is evident that the commoner forms have a wide range in 
more than one respect. Thus, for instance, Chironomus lobi- 
ferus is nearly an ubiquist as to distribution, and holophagous 
as to food. It should then follow logically that the most 
widely adapted forms are the most plastic; .that this plasticity 
will result in the numerical preponderance of the plastic form. 
Table 8 shows that many species are found under widely dif¬ 
fering conditions. Yet in every single case one habitat seems to 
olfer the optimal conditions, and it is in this habitat that the 
species attains its maximum representation. But it is rarely 
indeed that a plastic species dominates in its optimal habitat. 
What I mean to emphasize is that plasticity may insure con¬ 
tinuation of the species, but that it does not necessarily result in 
dominance. To illustrate, Chironomus digitatus and C. lobi- 
ferus are both plastic forms, the latter more so than the former; 
yet while both are very common in different areas, neither of 
the two dominates in any area, and their numerical total for 
the lake is inferior to that of many species that attain a local 
dominance. (See p. 480). 
Dominance is relative in each group. Twenty Hyalellae per 
square meter along the shore I would regard as a small repre¬ 
sentation, while an equal number for Leptocerus ancylus would 
mean dominance. Yet Hyalella dominates among the Crus¬ 
tacea of the shore, while Psephenus lecontei dominates among 
Coleopterous larvae. But no single species dominates among 
the biota of the shore line. Psychologically, any impression 
of dominance is linked to bulk,^—fifty Heptagenia larvae will 
look more numerous than a hundred Hyalellae,—so that an esti¬ 
mate can only be relative. 
No species dominates the biota of the entire lake. But for 
the plant zone the caddisworm Leptocella uwarowii comes 
nearest to complete dominance of any form in the lake, while 
Sialis infumata is prominent but not truly dominant in the dys- 
phytal area. In the aphytal area, however, we have a curious sim¬ 
ultaneous dominance of Corethra, Chironomus tentans, Protenth- 
es ehoreus, Corneocyclas, and of Limnodrilus and Tubifex. These 
biota of the aphytal area form a bigger contingent of the lake 
complex than nearly all other forms taken together. It is 
