52 Viscera of Insects. 



INTERNAL ANATOMY OF INSECTS. 



TKe muscles of insects are usually whitisli. Sometimes I 

 have noticed quite a pinkish hue about the muscles of the 

 thorax. They vary in form and position to accord with their 

 use. The mechanism of contraction is the same as in higher 

 animals. The ultimate fibers of the voluntary muscles, when 

 highly magnified, show the strice or cross-lines the same as do 

 the voluntary muscles of vertebrates, and are very beautiful 

 as microscopic objects. The separate muscles are not bound 

 together by a membrane as in higher animals. In ineects the 

 muscles are widely distributed, though, as we should expect, 

 they are concentrated in the thorax and head. In insects of 

 swiftest flight, like the bee, the thorax (Fig. 9, a, a a) is 

 almost entirely composed of muscles ; the esophagus, which 

 carries the food to the stomach, being very small. At the 

 base of the jaws the muscles are large and firm. The number 

 of muscles is astounding. Lyonnet counted over 3, 000 m a 

 single caterpillar, nearly eight times as many as are found in 

 the human body. The strength, too, of insects is prodigious. 

 There must be quality in muscles, for muscles as large as those 

 of the elephant, and as strong as those of the flea, would 

 hardly need the fulcrum which the old philosopher demanded, 

 in order to move the world. Fleas have been made to draw 

 miniature cannon, chains and wagons, many hundred times 

 heavier than themselves. 



The nerves of insects are in no wise peculiar so far as known, 

 except in position. As in our bodies, some are knotted, or 

 have ganglia, and some are not. 



The main nervous cord runs along the under or ventral 

 side of the body (Fig. 10), separates near the head, and after 

 passing around the esophagus, enlarges to form the largest of 

 the ganglia, which serves as a brain. From the brain many 

 nerves extend on each side to the compound eyes. The minute 

 nerves extend everywhere, and in squeezing out the viscera of 

 an insect are easily visible. 



The organs of circulation in insects are quite insignificant. 

 The heart is a long tube situated along the back, and receives 

 the blood at valvular openings along its sides which only per- 

 mit the fluid to pass in, when by contraction it is forced 

 towards the head and emptied into "the general cavity. Thus 

 the heart only serves to keep the blood in motion. According 



