4 
INSECTS IN GENERAL. 
sect’s body, called spiracles. The spiracles or breathing pores can be 
easily seen along the sides of all caterpillars which are not too densely 
covered with 'hairs. In the perfect or winged state of insects the 
branches of the air tubes are dilated into a great number of little ves- 
sicles or air bladders, which render their bodies lighter, and thus facili- 
tate their flight. 
In some aquatic larva; the trachea) project from the body in the form 
of little tufts, analogous to the gills of fishes. The aquatic beetles are 
under the necessity of rising to the surface, at intervals, for air, in a 
manner similar to that of the aquatic mammalia, the whales and the 
dolphins. 
THE DIGESTIVE OR NUTRITIVE SYSTEM. 
The digestive apparatus of insects, 
like that of other animals, consists of 
an elongated tube called the aliment- 
ary canal, extending through the body, 
and having a number of enlargements 
in its course, and in many insects pre- 
sents a particular resemblance to the 
digestive apparatus of birds. First, 
there is a short, straight oesophagus 
or gullet; this expands into a much 
larger cavity, resembling the crop; 
then follows a smaller muscular part, 
analogous to the gizzard ; and next, a 
much larger and longer cavity, which 
is the true digestive stomach; this be- 
comes contracted into the intestinal 
canal, which sometimes runs nearly 
straight through the body, and in other cases is more or less convolu- 
ted ; the intestine enlarges again before it reaches the end of the body 
into what is known as the large intestine or colon. As in other ani- 
mals, the alimentary canal is much longer and more capacious in the 
herbivorous than in the carnivorous kinds. As a general rule the canal 
is much more capacious in the larva than in the imago state. 
In Fig. 2, G, represents the digestive organs of one of the carnivo- 
rous beetles, Cicindela campestris; a the commencement of the oesopha- 
gus or gullet; c the crop ; d the gizzard ; e the stomach or principal di- 
gestive cavity'; / the commencement of the small intestine; h the large 
intestine; both of these parts are unusually short in this tribe of in- 
sects; m rn the convoluted vessels which are supposed to represent the 
liver of the higher animals. 
fFitt. 2.| 
Digestive organs of insects, explained in 
the text. 
