14 ENTOMOLOGY 



is not clearly ascertained, but it is thought that air is forced 

 into these tubes by pressure from the abdominal muscles, while 

 its escape through the spiracles is being prevented by the com- 

 pression of the stigmatal tracheae. 



The respiratory movements are entirely reflex and are inde- 

 pendent of the brain or suboesophageal ganglion, for they con- 

 tinue after decapitation and even in the detached a'bdomen of 

 a grasshopper or dragon fly. Each ventral ganglion of the 

 body is an independent respiratory center for its particular 

 segment. 



10. REPRODUCTIVE SYSTEM 



The sexes are always separate in insects, hermaphroditism 

 occurring only as an/ abnormal condition. The sexual organs, 

 situated in the abdomen, consist essentially of a pair of ovaries 



FIG. 178. FIG. 179. 



Reproductive system of male beetle, Melo Reproductive system of male 



lontha. a, accessory gland; c, copulatory Lepidoptera. a, accessory gland; 



organ; d, ejaculatory duct; s, seminal vesicle; d, ejaculatory duct; t, united 



t, testis; v, vas deferens. After KOLBE. testes; v, vas deferens. After 



KOLBE. 



or testes and a pair of ducts (oviducts or seminal ducts, respec- 

 tively). Primitively, the ducts open separately, as they still 

 do in Ephemeridse, but in nearly all other insects the two ducts 

 enter a common evacuating duct (vagina or ejaculatory duct) ; 

 this opens ordinarily between the penultimate and antepenulti- 

 mate segments of the abdomen, i. e., usually the ninth and 

 eighth, at any rate never through the last abdominal segment. 



