REPRODUCTION AND HEREDITY 147 



compare the simple, primitive armature of a male bristle-tail 

 such as a Machilid with the complex apparatus of a 

 hive-bee, or the still more elaborate structures found in a 

 moth or a muscoid fly (Fig. 38). These outer organs of repro- 

 duction, the action of which ensures the fertilisation of the 

 eggy are obviously of great importance to the life of the 

 individual and of the race. It is found that the details of 

 their structure and form are remarkably constant among 

 insects of the same kind differing in definite features from 

 those of nearly allied kinds (in Fig. 38 compare A, B 

 with D, E); the m^ale's structures are thus adapted to fit 

 or interlock with those of his mate so as to transmit the 

 sperms into her reservoir, whence as previously explained, 

 they are discharged as required for fertilisation of the eggs 

 when these are laid. 



The foregoing descriptions and discussions suggest that 

 the processes of inheritance and reproduction are closely 

 connected with the vital fact of sex-differentiation, and 

 reference has already been made in this chapter to some of 

 the differences of appearance and behaviour, apart from 

 those directly connected with the reproductive system, that 

 are often conspicuous in male and female insects respec- 

 tively. Well-known examples of such " secondary sexual 

 characters " are furnished by the brighter, richer, or more 

 vivid colours of many male butterflies, dragon-flies, and 

 other insects as compared with their mates, by the presence 

 of wings in a number of male cockroaches, grasshoppers, 

 moths, and Hymenoptera whose females are wingless, and 

 by the greater relative size and elaboration of sense-organs 

 in the male as compared with the female, as shown in the 

 larger compound eyes of male bees and many flies, the 

 elaborate feathered feelers of many male moths and gnats, 

 the immensely enlarged plate-like feelers, and the strange 

 head and body-outgrowths of many male chafers. Much 

 support is afforded by such facts to the well-known con- 

 tention of P. Geddes and J. A. Thomson (1889) that male 

 animals express in their organisation the active nature of 



