1912] Ephemeride N. yinphs Heptagenia Inter punctata ao 
are placed in an aquarium they mass together into clusters 
where they remain for many hours, and if recently collected, 
even days. As soon as a rock or any other object is placed in 
the water, the loose forms swim toward it, while considerable 
time often elapses before the masses are broken up. 
Two long bricks were placed one over the other in a basin of 
water and between them small pebbles varying 1n size so that 
the space gradually varied in thickness from one end to the other. 
Then a large number of nymphs were put in the water, and 
after a short time it was found that nearly all of the specimens 
were attached to the lower surface of the upper brick with their 
dorsal side downward, and a large majority of the specimens 
were in that portion of the wedge-shaped space where their 
backs came in contact with the brick below. 
Then a stone to which several nymphs were attached, was. 
placed in a tin pan and the temperature of the water was slowly 
raised. As the temperature approached 42°C. several speci- 
mens began to lose hold of the rock, others clung to it until the 
temperature reached 45°C. and in no case did the specimens. 
desert the stone until they were completely overcome by the 
heat. Then a large stone was placed in the pan, half of it being 
above the surface of the water. On top of this were placed 
other rocks highly heated and thus heating the stone half sub- 
merged, to which the specimens were attached. A piece of ice 
was kept in the water to keep it cool, while the temperature of 
the rock was quite high. This time the insects did not hug the 
rock as tightly as is their natural custom, but clung to it ina 
sort of half fast fashion. That, however, was not the only sign 
manifesting discomfort, as upon close observation it was noticed. 
that first one foot would be withdrawn from the hot rock and 
then another, the specimens clinging by four or five feet at a 
time and cooling the others. The space between the nymph 
and the rock would grow wider and wider until the insect would 
hang by only one or two claws and finally fall down backward to 
the bottom. As soon as refreshed in the cool water it would 
again attach itself to the hot rock. This same process was 
repeated over and over, though when long continued the rock 
was not sought with such extreme anxiety as in the beginning. 
Although most of the nymphs behaved in that way, occa- 
sionally one would leave the rock when the temperature of the 
stone was about 40°C. and would not return for a long time. 
