LIFE HISTORY OF HYDROUS ( HYDROPHILUS) TRIANGULARIS. 
11 
not enough water plants in the aquarium to work with. After these had been sup- 
plied she began to spin another case at 1.25 p. m. Assuming a position, back 
downward, her body almost parallel with the surface of the water and close to it, 
she held herself in place by means of the floating water plants (Potamogeton and 
Elodea), and moved her spinneret rapidly to and fro sidewise, at the same time 
pushing the material backward with her hind legs. After spinning the roof of the 
case in this manner for a few minutes she turned over without removing her spin- 
neret. Her body was considerably inclined, with her head some distance below the 
surface, and she opened her wing cases slightly to supply herself with fresh air at 
periods varying from 15 to 90 seconds, the shorter period the more common. This 
mode of taking in air through the lifting of the posterior ends of the elytra is in 
marked contrast to the method normally used (see p. 29). It required a longer 
period to make the floor of the case, since it is much more convex than the roof, 
Fig. 2— Longitudinal section 
through center of an egg case, 
showing a thick layer above the 
eggs, a floor beneath them, and 
an open chamber under the 
floor, in which the newly 
hatched larvse gather. 
Fig. 3.— End view of egg case, 
showing triangular plate with 
lunate opening beneath it. The 
floor beneath the eggs inside the 
case does not reach the side 
walls, leaving a free passage to 
the chamber beneath. 
but it was finished by 2 o’clock. The ends of the threads forming the floor were 
apparently fastened directly at either end to the previously completed roof, leaving 
a ridge or seam where the two joined. 
When the case was thus far completed, she began egg laying. The roof was 
covered on the inside with a thick layer of loosely woven silk inclosing large open 
spaces. From this layer the eggs were suspended with their long diameters vertical, 
each egg held in place by a thin meshwork of silken threads, which were attached 
to the thick layer above and to one another and formed a continuous floor below 
the egg mass (fig. 2) . 
At 2.15 she stopped laying and, after removing her spinneret, swam about 
for a time, evidently resting. On returning to the case it required several efforts 
to replace her spinneret in the open end, but once adjusted she began to weave the 
triangular plate across the upper part of the open end, leaving below it a lunate 
opening (fig. 3). The plate was considerably thicker than the rest of the case 
and was fastened on the inside to the layer of loosely woven silk that covered the 
