1912]  Ephemeride Nymphs Heptagenia Inter punctata 33 
toward the middle one, thus forming a sort of flexible paddle. 
When the swimming movements cease, the sete are again dis- 
tended, allowing the nymph to sink slowly to the bottom, or to 
take a short rest in suspension before another seemingly stren- 
uous effort at swimming is resumed. Short distances of two 
or three inches are usually made with alacrity, but a longer 
distance seems to fatigue the nymph and little progress is made. 
However, when shelter is in evidence the movement increases, 
and almost invariably the nymphs put on extra speed on the 
home stretch. 
May-Fly nymphs obtain their ogyxen from the water by means 
of the seven pairs of tracheal gills which are attached to the 
first seven abdominal segments. The nymphs would be quite 
inconspicuous in their natural habitat were it not for the simul- 
taneous backward and forward motion of the gills. While 
they are in a quiet attitude, all of the gills are not usually 
brought into play and their motion varies in proportion to the 
physical exertion, and to some extent at least, in proportion to 
the amount of food within the body of the nymph. The motion 
of the gills can be greatly increased by giving the nymph vigor- 
ous exercise and also by keeping it out of water for some time. 
Specimens destitute of nutrition for several days exercise their 
gills to a comparatively small degree. 
FOOD AND FEEDING. 
Ten active specimens were placed in separate dishes of 
water containing a bare rock, and after a few days of fasting, 
all chewed at a piece of alga when brought near to their mouth 
parts, as long as they were attached to a stone, finger, or some 
other object. It might be well to mention the fact that alge 
form the greatest share of the food of these nymphs and that 
animal food is not taken until the nymphs are well starved, 
when they chew at almost anything they come in contact with. 
When the stones were removed, the nymphs refused to eat 
unless the piece of food was large enough to afford attachment. 
Some of the nymphs ate almost immediately after coming in 
contact with the food, while others did not do so until after 
several days. Others again would attach themselves to smaller 
pieces of alga, but would not eat unless the particle of food was 
lightly pressed against their mouth part. Evidently the particle 
of food was too small to afford comfortable attachment and the 
