182 NEUROPTERA. 
space, these tiny tubes may serve to sepa- 
rate the ah' from the water. 
Some of the species remain only two 
years as larvae, while others continue so 
for five years. 
Lucy, And are they all alike in 
figure ? 
Mother, No, they differ as to size, 
and in some particulars as to shape ; but 
they have all a general resemblance, par- 
ticularly in the breathing fins, with which 
every species is famished. 
Lucy. Do they remain long in the 
pupa state ? 
Mother. It is necessary to observe, 
that in those insects, where the appearance 
of the pupa scarcely varies from that of 
the larva and the imago, this interme- 
diate stage of life is most usually called 
the nymph state. 
Most species of ephemera continue for 
three months in that state, the chief dif- 
ference of which from the larva is the 
acquisition of wings, nicely folded up 
under small cases next the thorax. 
