352 
TRANSFORMATIONS OF INSECTS. 
the bottom of the water, and shed their skins several times, and 
undergo their first metamorphosis during the spring. The fly does 
not make much use of its wings during the day, but is lively in 
the evening, and the females carry their bag of eggs suspended 
to their bodies. Some of the species are found in high northern 
latitudes, and appear over the snow at the very first approach of 
spring. Perla marginata , whose aquatic and perfect conditions 
are shown in the accompanying engraving, has two long articu- 
THE metamorphoses of Perla marginata. 
lated processes, something like those of the earwig. It is a 
common insect, and its larva, which is of a yellow citron colour 
spotted with black, is found in running streams and swiftly- 
flowing brooks. A closely allied species, the Nemoura , lives 
exactly in the same way as the Perla, but they are smaller 
insects. When young they have curious processes sticking out 
from the body, like those of the Perla, but they disappear in 
the perfect insect. The wings are always perfectly developed 
in the females, but they are short and rudimentary in the males 
