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 by Miall (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, v/ith 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 difi^er 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 



