I4O 



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 subcesophageal ganglion, for they con- 

 tinue after decapitation and even in the detached abdomen of 

 a grasshopper or dragon fly. Each ventral ganglion of the 

 body is an independent respiratory center for its particular 



segment. 



io. 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 

 lontha. a, accessory gland; c, copulatory 

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

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



Reproductive system of male 

 Lepidoptera. a, accessory gland; 

 d, ejaculatory duct; t, united 

 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 Ephemeridae, 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. 



