Of the families Belo- stomatidae, Nepidae, Corixidae and Hydrometridae have a pulsating sac at each knee-joint to assist the flow of blood through the legs, while in dragon-flies and locusts (Acridazdae) there is a ventral pulsating dia phragm, which forms the roof of a sinus enclosing the nerve-cords.
6) and their allies (Nepidae) dive and swim through the water.
The Nepidae breathe by means of a pair of long, grooved tail processes (really out-growths c, labrum; d, epipharynx.
In the Jurassic period many of the existing families, such as the Cicadidae, Fulgoridae, Aphidae, Nepidae, Reduviidae, Hydrometridae, Lygaeidae and Coreidae, had already become differentiated.
The Nepidae (fig.