CHAPTEK IL 

 GROWTH AND METAMORPHOSIS OF INSECTS. 



INSECTS are of distinct sexes, and besides males and fe- 

 males the social species, such as ants, wasps, and bees, are 

 largely represented by workers, which are undeveloped 

 females, not being normally capable of laying eggs. 



Insects differ sexually in that the female often appears to 

 have one abdominal segment less (one disappearing during 

 the semi-pupa state, when the ovipositor is formed). They 

 are also larger (except in the stag-beetles, some dragon-flies, 

 and certain bees), fuller, and duller-colored than the males; 

 while the latter often differ in sculpture and ornamenta- 

 tion and are more active flian the females. Certain female 

 moths are wingless,* the organs of locomotion as well as of 

 smell (antennas) and sight being better developed in the 

 male than in the female. The females of some water-beetles 

 (Dytiscus) have deeply-grooved elytra, or, as in Acilius 

 sulcatus, they are thickly set with hairs. 



Egg-producing Organs. With some notable exceptions 

 (i.e., cases of parthenogenesis), all insects develop from eggs, 

 which are formed in delicate tubes situated in the abdomen, 

 as in Fig. 4, ov. In the locust the ovaries consist of two 

 sets of about twenty long tubes, within which the eggs may 



* The only partial exception to the rule that the females are wing- 

 less while tlie males are winged is the male of two chalcids (West- 

 wood's Class. Insects, ii. 160). This fact was quoted by Darwin 

 (Descent of Man, i. 264). Darwin seems not to have been aware that 

 Newport figured these insects (Trans. Linn. Soc., xxi., Tab. VIII. p. 

 4) as Anthophorabia fasciata Newport and A. retusa Newport. The 

 mules also are without compound eyes, only a simple eye being 

 present in place of each compound one (Fig. 26). 



