140 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 trachez. 
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. 
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 
Bre. 178: Fic. 170. 
t 
a 
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; ¢, united 
t, testis; v, vas deferens.—After KoLBeE. testes; v, vas deferens.—After 
JKOLBE. 
or testes and a pair of ducts (oviducts or seminal ducts, respec- 
tively). Primitively, the ducts open separately, as they still 
do in Ephemerideze, 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. 
