General Review. 
In the pages preceding an attempt has been made to pre- 
sent the most important points now known about the biology 
of water bugs. It has been arranged to most readily determine 
what is known on any given form. To facilitate future work, 
the sexual differences of the various groups are figured. These, 
together with the drawings of the nymphs, permit a ready 
analysis of a survey of the pond at any time. The general 
reader is referred to the chapters on Ecologic and Economic 
Relations, and Form and Function, for matters of popular 
interest. 
In the developmental studies there have appeared certain 
points of note. The developmental changes of these bugs fall 
into two categories: First, characters acquired by the adult; 
second, characters. lost by the adult. 
Under the first may be mentioned the fact that ocelli, as a 
rule, when present at all, are adult characters. The toad bug 
is an exception to this, the nymphs possessing ocelli. The 
tarsus when two or three segmented is usually an adult charac- 
ter, the nymphs having one-segmented tarsi. Sometimes the 
adult possesses more segments in the antenne, as in Corixids. 
The sexual dimorphism of the adults, such as the asymmetry 
of male Corixids, etc., is, of course, attained only in the adult. 
On the other hand, in some instances of adaptation the 
adults lose structures present in the nymph. The best illus- 
tration, perhaps, is that of the Belostomatids, which have a 
single claw on front tarsus. The nymphs have two, one of 
which may get relatively smaller as later instars are reached. 
Another case is that of the hind claws of Notonecta and the 
Corixids. The first instar nymphs have two long claws, while . 
those of adult are setaform and obscured by the swimming 
fringe. These various changes are fundamental and signifi- 
cant. In determining phylogenetic relationships, the internal 
organization, combined with developmental changes, are most 
important in forms with incomplete metamorphosis. No 
staple arrangement of the Heteroptera can be made until much 
more is known of the biology of the group. 
(250) 
