High and low Dimorphism. 329 



tliis tliey do orily as concerns size aud the siippression of the secon- 

 dary sexual charaeters, because the structure of the keels on the 

 outer edge of the tibia of the hind leg, a non-sexual character, 

 ditfers more in the small species of Catharsius aiid Copris tban in 

 the large. 



In these two genera then the development of the secondary 

 sexual charaeters in the male is a function of the total size. and 

 they atford very good instances of high and low dimorphic 

 species. 



The next genus selected is Euckinis, a genus of the Melolon- 

 thidae. Here a totally ditìFerent structure is affected by the sexual 

 ditì'erentiatioD, namely the forelegs which in the males are immen- 

 sely elongated and fuvnished with antler-like tynes. E. longimanus 

 is the largest species kuown but with a wide range of Variation, 

 at any rate from SI mm. — 58 mm. in total length, and the pheno- 

 menou of high and low dimorphism is markedly appareut. 



From this species we pass by steps to the smaller forms E. 

 Macleayi and E. Par» i/i, and so to Proponaeus in which the size is 

 Nteadily reduced, aud in correspoudence the ratio betweeu the total 

 length and the length of the forelegs becomes also reduced, so 

 that in the last naraed form, which diifers generically in unimpor- 

 tant details from Euchirits, the forelegs of the male bave very 

 closely approached those of the female in proportions and structure. 



In the next two genera selected, Golofa and Dyìiastes, members 

 uf the Dynastidae, we obtain excellent series, in which the males 

 of the larger species of the genera as respects the thoracic and 

 ••lypeal horns are high in comparison to the smaller species. In these 

 cases we will give average measurements made up from a series 

 '»f measurements for each species which iueluded the extreme types 

 as well as the average condition. 



In Golofa we bave: 



Mean body length Mean ratio Bod^length 



Thoracic horn 

 Elytron length 



