34 Journal New York Entomological Society. fv°'- ^^i- 



the specific gravity of the creature, and thus assisting it in floating. 

 The body of a whirligig is hairy beneath; the air entangled in the 

 hairs in part supports the beetle on the surface, and permits of its 

 evolutions. A muscular effort is necessary to send many water beetles 

 below the surface, and their claws are required to keep them below, 

 grasping some water plant. This is illustrated in the floating to the 

 surface of Hydrochus and Helophorus, when the water net disturbs 

 their grip on aquatic plants. With others, as the Dytiscidas, the 

 escape of the air from beneath the elytra increases their specific 

 gravity and their descent is thereby facilitated. The bubble of air 

 seen at the anal extremity as a Dytiscid disappears beneath the water 

 is an expelled bubble, not one that is to be inhaled. In short, the phe- 

 nomena and structural modifications heretofore assumed to be con- 

 nected with respiration are, at least in great part, connected with 

 flotation or maintenance of equilibrium. 



Respiration is according to Brocher effected in Haliplidae and 

 Dytiscidse by drawing in air through the last two abdominal stigmata, 

 and expelling it through the other stigmata, particularly the anterior 

 pair. He has detected in Cybister and less distinctly in other genera 

 air pockets in the midst of the muscular masses of the meso-thorax 

 and meta-thorax, which are connected directly with these anterior stig- 

 mata, and explain their larger size, but he expresses an opinion that 

 no large quantity of air is habitually stored therein, the action of 

 respiration being in these beetles rather a thorough ventilation of the 

 whole tracheal system. The arrangement of the stigmata and their 

 relation to the extraordinarily enlarged coxal plates is illustrated in 

 the September number of our Journal. In other aquatic insects, and 

 especially those which do not come to the surface frequently to breathe, 

 but remain below the surface for long periods, even for weeks at a 

 time in some cases, a complicated system of pubescence serves to 

 supply the small quantity of air required by comparatively inactive 

 creatures, and to permit of this supply being obtained from aquatic 

 plants or from the aerated waters of rapid streams. The simple hy^ 

 drofuge pubescence, consisting of hairs set nearly perpendicular to 

 the body and designed simply to retain a body of air, is replaced by a 

 double arrangement of hairs ; one series is curved so as to become 

 parallel to the body and applied one above the other, like shingles, 

 whereby a sheath-like enclosure of the body is effected, and a second 



