SEX-CHARACTERS ILLUSTRATED 59 



peculiar transformations of structures, but in 

 a more diffuse way affecting the size (females 

 being usually larger), the proportions of 

 parts, the colour (males tending to be more 

 brilliant), and other features, or in numerous 

 little ways giving a slightly different turn to 

 the analogous organs in the two sexes. 



It is usual to classify the differences between 

 the sexes as " primary " and " secondary," to 

 which some would add " tertiary." The 

 " primary " differences refer to the repro- 

 ductive organs, the " secondary " to those 

 that appear in other parts of the body, such 

 as the larynx or the hair. A clearer scheme 

 of division, slightly modified from Poll's and 

 Kammerer's table, may be thus expressed 



SEX DIFFERENCES 

 I. ESSENTIAL. 



In the gonads ovaries and spermaries. 

 II. ACCESSORY OR INCIDENTAL. 



(a) Subsidiary to the gonads : 



internally, as in accessory glands ; 

 externally, as in pairing or egg- 

 laying organs. 



(ft) Somatic and extra-genital : 

 internally, as in vocal organs ; 

 externally as in colour, hair, 

 feathers, etc. 



It is evident that most of these sex-differ- 

 ences have both a structural and a functional 

 side, a morphological and a physiological 

 aspect; but for practical purposes one side 

 may often be disregarded. Thus a chitinous 

 decoration or instrument on a male beetle 



