252 Anatomy and Physiology of the Family Nepida, ‘March, 
in front of the body, which throws the center of gravity too fr 
forward for convenient flight. 
When preparing for flight the air sacs are first inflated, the 
prothorax and head are thrown downward, and the front legs dis- 
posed of in a very ingenious manner. The femurs are bent upon 
the joint near the head, a little more than go° from their origina 
position, and the tibiæ are folded closely against these, thus the 
front legs hang under the body, directed a little backward. 
Though of much smaller size, Perthostoma strongly resembles 
Belostoma in general appearance, but is quite distinct in anteng, 
beak and legs. The females of the genus carry their eggs on the 
back, regularly arranged in a single layer, cemented to the body 
by a substance insoluble in water. The eggs of the other genera 
are attached to the water plants and submerged objects. 
Belostoma, Perthostoma and Ranatra are infested by 4 Hy- 
drachna, which is found attached to different parts of the body 
This is probably also true of Nepa, but I have not had the spe 
mens to determine. For a fuller account of the external anatom) 
and the family characteristics, the reader is referred to the at 
on systematic entomology, while attention is now called to 
internal anatomy. ' 
. A. THE FUNCTION oF NUTRITION. pe 
The function of nutrition includes all the processes pe sol 
in preserving the organism of an animal, as the digestion ai 
its conveyance to a point for use, the chemical changes : 
verting food into tissue, and the removal of waste matter “| 
a ction of circle 
processes are carried on by the organs of digestion, a 
tion, of respiration and of excretion, which form separate ; 
heads for consideration. 
I, THe DIGESTIVE SYSTEM. ee 
15 
On opening the insect the most prominent set of organs mr 
alimentary canal and its appendages. The thread-like the bek 
characteristic of suctorial insects, extends straight from stoma 
to the metathorax, where it enlarges abruptly into the pecali | 
The anterior end of the cesophagus is connected a vision 
pumping apparatus, which will be described later. The © et 
the digestive apparatus into a distinct crop, chylific 
frequently found among insects, is practically oblit je 
insects; this, indeed, is the case in most of the i pegit 
Sometimes in Ranatra an oval enlargement exists at 
a 
