DARWINISM ATTACKED. 107 



Such are the metallic purple and bronze colours of the male 

 grackles compared with the dull brown of the females ; the 

 long tails and brilliant coloration of the male pheasants, 

 the great, spreading, patterned tail of the peacock, the 

 larger size or the winglessness of many female insects, etc. 

 All these differences between male and female of the same 

 species of animal, beyond or in addition to the differences 

 between the actual primary reproductive organs, are known 

 as secondary sexual differences, or the characters themselves, 

 which may be characteristics of physiology and habit as 

 well as the more familiar ones of structure, are called sec- 

 ondary sexual characters. The layman may not readily 

 appreciate the abundance and the great variety of these char- 

 acters, but it is a fact that almost all species of animals, 

 excepting those in the lower invertebrate branches, show 

 them, and if one will try to recall the aspect of the two 

 sexes in one after another of the species of animals with 

 which one is familiar, mammals, birds, insects, etc., one will 

 begin to realise how widespread and significant are these 

 secondary sexual characters. 



Various biologists have made up classifications, from 

 various points of view, of the different kinds of these char- 

 Classifications acters ' one classification, like that of Kramer * 

 of secondary sex- for the secondary sexual characters of insects, 

 Tial characters, n thfi different parts of the body 



showing the differences between male and female indi- 

 viduals, as head, antennae, thorax, wings, legs, abdomen, 

 etc., and on the character of the differences themselves, as 

 whether differences in structure or in colour and pattern. 

 Another type of classification, and one more useful for our 

 present discussion, is that based on the apparent significance 

 or actual use of the differing characters. An excellent 

 classification of this type is that of Plate. 2 The following 

 are the principal subdivisions of this classification with a 

 few examples illustrating each : 



