182 



PERIPATUS, MYRIAPODS, AND INSECTS. 



The series of rings of which the external crust or skeleton of 

 Insects is composed exhibits great modifications, not only in the 

 various kinds of Insects, but even in the different parts of the 

 same individual, and at successive periods of its development. 



Many of the anatomical structures have positions in the body 

 that are fairly constant throughout the class. Parts of the respira- 

 tory and muscular systems and 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 



Fig. 12. — Diagram of Exterior of Insect. 

 The two vertical dotted lines indicate the division between H., Head; 

 T., Thorax; and A., Abdomen, a, Antennse ; h, Labrmn ; c. Mandible; 

 d. Maxillary palpus ; e. Labial palpus ; /, Facetted eye ; g, Pronotum ; h, 

 Mesonotum ; f, Metanotum ; /•, Wings; l\ to /lo, Abdominal segments; 

 w, The internal membranous portions uniting the apparently separated seg- 

 ments ; «, Cerci ; o. Stigma ; /, Abdominal pleuron bearing small stigmata ; 

 q\, qz, ql. Pro-, meso-, and meta- sterna; r, Metathoracic episternum ; 

 s, Epimeron, these two forming the mesopleuron ; r2, S2, Metathoracic epi- 

 sternum and epimeron ; /, Coxa ; v, Trochanter ; iu. Femur ; x, Tibia ; 

 y, Tarsus ; s, Gula. 



system are below the alimentary canal, except that the brain is 

 placed above the beginning of the canal in the head. Fig. 13 

 shows the arrangement of some of the chief organs of the body, 

 with the exception of the muscular and respiratory systems, and 

 the fat-body. 



