390 The Philippine Journal of Science 



the Sozan. Here also they live on a rapid current, but at Shinten 

 only the males and the nymphs of the last instar were found. 

 The nymphs were not seen at Sozan. 



The considerable length of the first joint of the antennae and 

 of the intermediate and posterior femora has been acquired in 

 all probability as an adaptation to the habitat of this insect. 

 The fringe of long hairs on the intermediate tibiae seems of 

 service in keeping the insect from getting wet. This character 

 is also found in Halobates, which inhabits the sea. In the 

 females of Ptilomera, a similar fringe occurs on the intermediate 

 femora. The peculiar abdominal structure in the female of 

 this insect seems to have some adaptive significance to its life 

 on running water; at copulation the rolled-up lateral margins 

 firmly clasp the abdomen of the mate on the back. The copul- 

 atory organs of both sexes are entirely enveloped by the tube- 

 like anal segment of the female. The insects when captured 

 in copula and placed in a small vial continue the act for a fairly 

 long time, contrary to any other species of the Gerridae known 

 to me. 



