STRUCTURE, GROWTH AND ECONOMICS OF INSECTS 



19 



{Tremex columba); the saw flies have the inner plates united to form 

 the egg channel, the upper plates form a sheath, while the lower have 

 serrate edges and are wielded Hke a saw, making slits in leaf or stem 

 for the deposition of the eggs. In the stinging hymenoptera the 

 ovipositor is modified to form a sting; the upper valves of the honey 

 bee are soft, forming a pair of palpi, the inner lobes form a sheath, 

 and the ventral lobes are represented by a pair of barbed darts. The 

 poison is of two kinds, one alkaline the other 

 acid, and is secreted by glands within the 

 abdomen. 



INTERNAL ANATOMY 



The internal anatomy of an insect may 

 be discussed under the following heads: {a) 

 muscular system; {b) respiratory system; 

 (f) circulatory system; {d) intestinal or 

 digestive system; {e) nervous system; (/) 

 reproductive system (Fig. 25). 



(a) Muscular System. — The muscular 

 system xif insects is well developed. The 

 muscles are attached to the inner surfaces 

 of the exoskeleton. 



In the abdomen the arrangement of 

 th.e muscles is the same in each segment, 

 except at the extremity where special mus- apparatus of honey bee. ag., 



^ . . -^ ^ . Accessory gland; p., palpus; 



Cles exist for moving the ovipositor, the pg., poison gland; r.. reser- 



cerci or other terminal organs. In the ^ J^ ;'" ^^"'^- ^'^^^''' ^"''' 

 sternum of each abdominal segment there 



are one or two sets of longitudinal muscles on each side of the nerve 

 chain. These are the longitudinal sternals or ventral recti (Fig. 26). In 

 the tergum also similar sets of muscles occur on each side of the dorsal 

 vessel; these are the longitudinal tergals or dorsal recti. Between these 

 longitudinal muscles and the integument are numerous oW/g«e and trans- 

 verse muscles, and these, with the longitudinal muscles, bring about the 

 various turning, wriggling or telescoping movements of the abdomen. 

 In each abdominal segment there are also two muscles which pass 

 from the tergum to the sternum. These are the tergo-sternals which 



Fig. 24. — Sting and poison 



