PLECOPTERA NYMPHS OF NORTH AMERICA 9 
Schoenemund (44) reports that the female nymph of Perla 
cephalotes sheds its skin thirty-three times before reaching ma- 
turity ; eighteen times during the first year, nine during the sec- 
ond, and six times during the third year. The male nymph, he 
says, being much smaller, passes through fewer instars than the 
female. However, according to Samal (43) both male and female 
nymphs of P. abdominalis have an equal number of molts. The 
nymphs are less active in cold weather than when it is warm, but 
they feed more or less during the entire winter. Molting is less 
frequent during cold weather, and the nymphs cease feeding 
during the process of ecdysis. There is a period of several days 
before the mature nymphs emerge when they take no food what- 
soever, and such nymphs will usually be found to have an empty 
digestive tube. 
COLLECTING, TRANSPORTING, AND REARING 
STONEFLIES 
Collecting stonefly nymphs is rather a simple matter. Where 
only a few specimens are sought, or where only a superficial 
qualitative survey is to be made, nymphs can usually be procured 
by hand picking. The large nymphs of Perla, Acroneuria, and 
others will be found chiefly in the large swift-water streams where 
‘they occur underneath the stones. Upon quickly lifting such 
stones out of the water, the nymphs often remain attached to the 
underside, and can then readily be taken. 
In the smaller streams or in the upland brooks which are in- 
habited by Pteronarcys, Peltoperla, Nemoura, Leuctra, and oth- 
ers, the nymphs are found among the leaf drifts and in the debris. 
A handful or two of such debris will usually yield several speci- 
mens. Since the nymphs which occur in these smaller streams 
are mostly concolorous, they so nearly harmonize with the color 
of the dead leaves and sticks that they are not easily recognized. 
It is well, therefore, to spread out the debris on a flat surface or 
in a pan, and earefully search out the nymphs, especially the 
smaller ones, which often can be detected only after they start 
moving around. The most efficient manner in which to obtain the 
smaller forms is to bring a good supply of trash to the labora- 
tory where it can be spread out in a large shallow pan in a little 
water. The nymphs soon start to crawl about and are then easily 
picked out. 
Where a large number of specimens is to be collected, or when 
a thorough qualitative collection is to be made, it becomes desir- 
