THE SECRETORY AND MUSCULAR SYSTEMS. 
5 
THE SECRETORY SYSTEM. 
The secretory apparatus of iusects, though analogous in function, is 
very different in appearance from that of the higher animals. Instead 
of solid glands, like the liver or kidney, it has the form of masses of 
convoluted tubes, as represented at m in the preceding figure. The sal- 
ivary glands, the liver, the kidneys, and the testacies are found repre- 
sented in iusects. The gastric and pancreatic fluids are secreted by 
little cells or follicles in the coats of the stomach. 
THE MUSCULAR SYSTEM. 
The muscles of insects, like those of other animals, consist of con- 
tractile fibres, but in their situation and attachments, as compared with 
those of the vertebrate animals, they are reversed ; that is to say, in 
the latter, the muscles are situated outside of, and upon the bones, 
which constitute the supporting part of the body, whereas in insects, 
the supporting part is the external crust, and the muscles are attached 
to its internal surface. The muscles are of a pale yellowish color, and 
are usually presented in the form of thin layers, and sometimes of iso- 
lated fibres, and are never united into the rouuded compact form which 
they have in the higher animals. By counting the separate fibres, a 
very great number of muscles have been enumerated. Lyonet counted 
nearly four thousand in the larva of Gossus ligniperda, and Newport 
found an equal number in the larva of Sphinx ligustri. The muscles of 
insects possess a wonderful contractile power in proportion to then- 
size. A Ilea can leap two hundred times its own length, and some 
beetles can raise more than three hundred times their own weight. This 
remarkable strength may probably be attributed to the abundant sup- 
ply of oxygen by means of the myriad ramifications of the air tubes. 
THE ORGANS OF THE SENSES. 
Insects are evidently endowed with the ordinary senses which other 
animals possess, but no special organs of sense, except those of sight, 
have been discovered with certainty. 
Sight . — The eyes of insects are of two kinds, simple and compound. 
The simple or single eyes are called ocelli, and may be compared in ap- 
pearance to minute glass beads. They are usually black, but sometimes 
red, and are generally three in number, and situated in a triangle on the 
top of the head. In iusects with a complete metamorphosis, these are 
the only kind of eyes possessed by them in their larva state, and in 
these they are usually arranged, in a curved line, five or six in number, 
on each side of the head. We have noticed that in some insects which 
undergo only a partial metamorphosis, as for example the common 
