THE WATER CABINET. 141 
The Notanecta, or Boat-fly, is a rapacious creature, that 
spends much of its time lying in wait for prey, but which 
exhibits immense activity when it captures its booty, 
darting down with it, and holding it firmly by the fore- 
legs, which are formed as claws. It is ingeniously 
adapted for the predaceous aquatic life it leads; the 
general form is well adapted for propulsion through 
water, and the hinder legs have an oar-like form, and are 
fringed with bristles along the edge, by which their 
striking surface is much increased. The boat-fly is an 
artistic swimmer ; it varies its motions considerably, and 
delights in swimming on its back, a feat in which it is 
aided by its eyes being so placed as to enable it to see 
both above and below, and thus gain early intelligence of 
danger, or of the approach of its prey. Owing to their 
liveliness and voracity, they afford much interest when 
domesticated, and should be treated as directed for 
Dytiscus. ; 
The Water Scorpion is a good representative of the 
Nepide, and has the distinguishing features of its tribe 
very strongly marked. The Water Scorpion is a very 
common inhabitant of our brooks, and its singular form 
quickly arrests the eye of the sportsman when turning 
over the contents of the drag-net. N. neptunia and 
N. cinerea are, perhaps, the most common ; and either of 
these is an admirable object for the microscope. The 
water-scorpion is the victim of the parasitic water-mite 
(Hydrachna abstergens), which inserts its egg in the 
body of the Nepa, and thus compels it to support the 
young of its worst enemy, a task which it performs at the 
