HEXAPODA . 
69 
one in each segment, between the alimentary canal and the layer of 
muscles of the ventral side of the body; the two cords connecting 
these masses, or ganglia, pass one on each side of the oesophagus to 
the brain. The reproductive organs (r) lie in the cavity of the abdo¬ 
men and open near the caudal end of the body. The respiratory 
organs are omitted from this diagram for the sake of simplicity. 
The Muscular System .—We find in insects a wonderfully large 
number of muscles. Those that move the segments of the body form 
several layers just wit.iin the body-wall. The two figures on Plate II 
represent two caterpillars which have been split open lengthwise, one 
on the middle line of the back and one on the opposite side; in each 
case the alimentary canal has been removed, so that only those organs 
that are attached quite closely to the body-wall are left. From a study 
of these figures some idea can be obtained of the number and arrange¬ 
ment of these muscles. It should be borne in mind, however, that 
only a single layer of muscles is represented in these figures—the layer 
which would be seen if a caterpillar were opened in the way indicated. 
When these muscles are cut away many other muscles are found ex¬ 
tending obliquely in various directions between these muscles and the 
body-wall. 
The muscles of insects appear very differently from those (the lean 
meat) of higher animals. In insects the muscles are either colorless 
and transparent, or yellowish white ; and they are soft, almost of a 
gelatinous consistence. When hardened by alcohol or otherwise, and 
examined with a microscope, they are seen to be crossed by numerous 
transverse lines, like the voluntary muscles of Vertebrates. 
As a rule, the muscles of insects are composed of an immense 
number of distinct fibres, which are not enclosed in tendinous sheaths 
as with Vertebrates. But the muscles that move the appendages ol 
the body are furnished with a tendon at the end farthest from the 
body (Fig. 81). 
Fig. 8i.— Leg of May-beetle. (After Straus-Durcklieim.) 
Notwithstanding the soft and delicate appearance of the muscles 
of insects, they are leally very strong. One has only to observe the 
power of leaping possessed by many species to be convinced of this. 
