HEXAPODA. 69 



one in each segment, between the alimentary canal and the layer of 

 muscles of the ventral side of the body ; the two cords connecting 

 these masses, or ganglia, pass one on each side of the oesophagus to 

 the brain. The reproductive organs (r) lie in the cavity of the abdo- 

 men and open near the caudal end of the body. The respiratory 

 organs are omitted from this diagram for the sake of simplicity. 



The J\fiiscitlar System. We find in insects a wonderfully large 

 number of muscles. Those that move the segments of the body form 

 several layers just within the body-wall. The two figures on Plate II 

 represent two caterpillars which have been split open lengthwise, one 

 on the middle line of the back and one on the opposite side ; in each 

 case the alimentary canal has been removed, so that only those organs 

 that are attached quite closely to the body-wall are left. From a study 

 of these figures some idea can be obtained of the number and arrange- 

 ment of these muscles. It should be borne in mind, however, that 

 only a single layer of muscles is represented in these figures the layer 

 which would be seen if a caterpillar were opened in the way indicated. 

 When these muscles are cut away many other muscles are found ex- 

 tending obliquely in various directions between these muscles and the 

 body-wall. 



The muscles of insects appear very differently from those (the lean 

 meat) of higher animals. In insects the muscles are either colorless 

 and transparent, or yellowish white ; and they are soft, almost of a 

 gelatinous consistence. When hardened by alcohol or otherwise, and 

 examined with a microscope, they are seen to be crossed by numerous 

 transverse lines, like the voluntary muscles of Vertebrates. 



As a rule, the muscles of insects are composed of an immense 

 number of distinct fibres, which are not enclosed in tendinous sheaths 

 as with Vertebrates. Rut the muscles that move the appendages of 

 the body are furnished with a tendon at the end farthest from the 

 body (Fig. 81). 



FIG. 81. Leg of May-beetle. (After Straus-Durckheim.) 



Notwithstanding the soft and delicate appearance of the muscles 

 of insects, they are really very strong. One has only to observe the 

 power of leaping possessed by many species to be convinced of this. 



