THE SECRETORY AND MUSCULAR SYSTEMS. 



THE SECRETORY SYSTEM. 



The secretory apparatus of iusects, though analogous iu functiou, 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 insects. 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 iu 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 iu the form of thin layers, and sometimes of iso- 

 lated fibres, and are never united into the rounded 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 Cossus Ugniperda^ and Newport 

 found an equal number in the larva of Sphinx Ugustri. The muscles of 

 insects possess a wonderful contractile power in proportion to their 

 size. A flea 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 insects 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 iu a curved line, five or six in number, 

 on each side of the head. We have noticed that in some iusects which 

 undergo only a partial metamorphosis, as for example the common 



