MUSCLES I I 5 



!Many of the anatomical structures have positions in the body 

 that are fairly constant throughout the class. Parts of the 

 respiratory and muscular systems and the fat-body occur in most 

 of the districts of the body. The heart is placed just below the 

 dorsal surface ; the alimentary canal extends along the middle 

 from the head to the end of the body. The chief parts of the 

 nervous system are below the alimentary canal, except that the 

 brain is placed above the beginning of the canal in the head. 

 The reproductive system extends in the abdomen obliquely from 

 above downwards, commencing anteriorly at the \ipper part and 

 terminating posteriorly at the lower part of the body cavity. 



In Fig. 63 we show the arrangement of some of the chief 

 organs of the body, with the exception of the muscular and 

 respiratory systems, and the fat-body. It is scarcely necessary 

 to point out that the figure is merely diagrammatic, and does not 

 show the shapes and sizes of the organs as they will be found in 

 any one Insect. 



Muscles. 



The muscular system of Insects is very extensive, Lyonnet '^ 

 having found, it is said, nearly 4000 muscles in the caterpillar 

 of the goat-moth ; a large part of this number are segmental 

 repetitions, nevertheless the muscular system is really complex, 

 as may be seen by referring to the study of the flight of dragon- 

 flies by von Lendenfeld.^ 



The minute structure of the muscles does not differ essentially 

 from what obtains in Vertebrate animals. The muscles are 

 aggregations of minute fibrils which are transversely striated, 

 though in variable degree. Those in the thorax are yellow or 

 pale brown, but in other parts the colour is more nearly white. 

 The muscles of flight are described as being penetrated by 

 numerous tracheae, while those found elsewhere are merely 

 surrounded by these aerating tubules. 



The force brought into play by the contractions of Insect muscles 

 is very great, and has been repeatedly stated to be much superior 

 to that of Vertebrate animals ; very little reliance can, however, be 



^ Lyonnet, Traite anatomiqtie de la ChenilU qui range h hois de SauU. La 

 Haye, 1762. On p. 188 he says that he found 1647 muscles, without counting 

 those of the head and internal organs of the body. He puts the number found in 

 the human body at 529. 



2 SB. Ak. Wien, Abth. 1, Ixxxiii. 1881, pp. 289-376. 



