436 PHYSIOLOGY OF THE INVERTEBRATA. 



or " breathing-slits." These sounds are said to give rise to 

 various emotions — fear, anger, and love ; consequently the 

 musical sounds produced by " wing-beating " and the " vocal 

 organs " are material agents in the reproduction of many 

 Insecta ; for it should be borne in mind that those females 

 which are mute always " alight near " * the musical males, 

 and many insects (of either sex) know the particular notes 

 of their kind.f 



From what has been said in the last few pages, it will be 

 seen that odours, colours, dances, and music are important 

 agents in bringing about sexual reproduction in many orders 

 and genera of the Insecta. 



We now consider the subject of parthenogenesis or virginal 

 reproduction, which occurs in certain insects. In Chermes 

 dbietis and Coccus hesperidum, the females produce ova which 

 give rise only to females, for no males have been discovered. 

 In the Aphidce both sexes are developed in the autumn; 

 these copulate, when the females lay eggs, which are hatched 

 in the following spring. But instead of producing individuals 

 of both sexes, these eggs give rise only to female insects, 

 which produce living young without any congress with the 

 male; the brood thus brought forth again produces living 

 young in the same manner, and this goes on throughout the 

 whole summer, without the appearance of a single male 

 insect. In the autumn again, male and female individuals 

 are produced, the latter lay eggs which are to continue the 

 species until the following summer. The production of 

 parthenogenetic females has no definite limit, but is regulated 

 to a certain extent by temperature and food supply. To 

 retain the parthenogenetic function, the Aphidce require 

 warmth and a plentiful supply of food ; for on the failure of 

 either of these conditions the parthenogenetic females give 

 rise to both males and females' The genital organ of a 



* Darwin's Descent of Man, vol. i, chap. lo. 



t For further information, see Swinton's Insect Variety, pp. 102-229 ; and 

 Von Siebold's Invertebrata, p. 406. 



