LIFE HISTORY OF HYDROUS ( HYDROPHILUS) TRIANGULARIS. 
25 
of the body might easily give it a distorted shape; but the pupa protects itself from these dangers by 
assuming an unusual attitude. It extends itself back downward in a horizontal position and supports 
the weight of its body by the three sets of hooks as upon a tripod. In this attitude, though surrounded on 
all sides by moist earth, it keeps its body from actual contact with any object until it has assumed its 
final shape. 
These observations on the attitude of the pupa and the use of the hooks were 
confirmed later byMiger and Lancret (1809), and are quoted byMiall (1895, p. 73). 
They may be true of the European H. piceus, but the American species here described 
certainly rests in the pupal chamber with the back uppermost, as noted by Matheson 
(1914, p. 343). 
Furthermore, the body is strongly curved upward instead of being horizontal, 
so that the central portion is lifted still farther above the floor of the chamber (fig. 
15). The reason for this, as well as another use for the spines, was revealed on 
digging out some of the pupae just after a heavy rainstorm. Two of the pupal 
chambers were found partly flooded with water, but the pupae, resting upon their 
spines, with their backs strongly arched, had thereby kept their spiracles well 
above the water and so prevented drowning. 
The scutellum stands out prominently on the dorsal surface of the second 
thorax segment, the elytra being drawn away from it onto the ventral surface. 
These elytra pads each show four distinct longitudinal ridges beside the two margins, 
with broad intervening furrows. The pads of the true wings are smooth. These 
four pads are apparently fastened in position by being cemented to the outside of 
the pupa case, and also to the outside of the cases covering the second and third 
legs. In only one instance was this cement loosened after preservation in alcohol. 
At the posterior end of the last segment is a pair of large cerci 4.25 mm. in 
length. Each is cylindrical, considerably enlarged at the base for a third of 
its length and then abruptly narrowed and of the same diameter for the rest of 
its length. Both portions are transversely wrinkled, and the tip is armed with a 
short bipartite claw, one or both of the rami being often toothed (fig. 18). These 
cerci are also part of the pupa case and are left in the pupal chamber when the 
beetle emerges. They are muscular, with considerable freedom of motion, and 
evidently serve the pupa partly as false legs for support in connection with the 
anterior spines and partly as a means for adjusting its position in the chamber. 
If a pupa is inverted in the pupal chamber, it can right itself by means of convul- 
sive movements of these cerci, together with the posterior abdomen, the latter 
supplying the muscular power and the cerci furnishing the point of leverage with 
their sharp claws against the walls of the chamber. If the pupa is disturbed, it 
simply kicks itself about vigorously, using the abdomen and cerci in the same 
manner. 
It is worthy of note that all the hydrophilid pupae formed in earth chambers 
are similarly provided with cerci, although these differ in structure in the various 
species. 
During the transformation from the larva into the pupa the mode of respira- 
tion is changed. The larva breathes through the posterior openings of the tracheal 
trunks, as already described, but these disappear in the pupa and in their place 
fully developed spiracles appear along the sides of the thorax and abdomen, as in 
