no DARWINISM TO-DAY. 



primary one, that is, indicate an older phyletic condition, as 

 the absence of antlers in the female deer ; or be a secondary 

 one, that is, gradually acquired by progressive reduction, as 

 the loss of wings by many female insects. 



Sub-group 3. Atavistic characters, as the more marked hairiness 

 on the breast of men as compared with women. 



Sub-group 4. Correlated characters, which may be called into ex- 

 istence by other organs present ; with the female mollusc 

 Anodonta, the shell is more strongly bowed in adaptive 

 correlation with the expanded brood chamber between the 

 gills. 



Sub-group 5. A large number of secondary sexual characters 

 which are incapable of specific classification, as the minute 

 differences between the sexes in size and habitus; slight dif- 

 ferences in wing form in humming-birds, dragon-flies, and 

 butterflies ; small differences in character and number of 

 tarsal and antennal segments of many insects. 



As Plate justly remarks the foregoing classification can, 

 of course, make no pretension to completeness. But it 

 . indicates sufficiently clearly certain important 

 nificance of the differences among the secondary sexual char- 

 acters ; differences especially important in con- 

 nection with any attempt to get at an explanation of the 

 why and how of these characters. Such a classification 

 shows that many of these characters have uses which are 

 of a kind directly helpful in the struggle for existence, as the 

 strong antlers of the stags, useful in defence against attacking 

 enemies ; the brood sacs of the kangaroos and opossum, use- 

 ful in caring for their helpless young; the milk-glands and 

 teats of all female mammals, the pollen-baskets and wax- 

 glands of the honey-bee which make the workers more 

 effective food-gatherers and food-storers, and the protective 

 colours and patterns of many insects and birds. But others, 

 many others, indeed, of these secondary sexual characters, 

 are either of a kind apparently useless in the struggle for 

 life, or even of a kind actually harmful. Of apparent useless- 

 ness are the reduced wings of some male insects, and the 

 host of slight differences in coloration, pattern, size, or 



