LIBRARY

216
COLLEGE ENTOMOLOGY
potentialities of mayflies and show why the naiads constitute one of the most
important and stable foods of fresh-water fishes, aquatic insects, and other
small animals. Their reproductive capacity must be exceedingly great to enable
such helpless creatures to survive at all. However, Tillyard (1926) states
that certain species in New Zealand are threatened with extermination by
the introduction of the European brown trout and the American rainbow
trout.
External anatomy. - Some of the most striking anatomical features of the
adults have already been given. The compound eyes are largest in the males,
FIG. 78. Naiads of mayflies. A. Calli/};etis fluctuans (Walsh); B. Prosopjstoma foliaceum
Fourcroy. dorsal and ventral aspects; C, Ephemerella grand is Eaton; D, Paraleptophelbia packii
(Needham); E. Siphlonurus occidentalis Eaton; F, Iron /ongimanus (Eaton) (A after Morgan,
1913; B after Eaton, 1883-8; C-F after Needham, 1927.)
and in certain genera the facets of the upper portions of the eyes in both sexes
are larger than those of the lower. There is a division of the eyes in Cloifon,
which, the upper portions being elevated upon tubercles, are said to be pillared
or turban-eyed. The three ocelli are between the compound eyes. The mouth
parts of the adults are aborted or weakly developed, indicating that the mature
forms do not take nourishment. The pro- and metathorax are small, whereas
the mesothorax is large and well developed to motivate the insect in its brief
B