The Evidence from Sexual Characters. 193 



and they are not known to be used by the males infight- 

 ing with each other. The conclusion which best agrees 

 with the fact of the horns having been so immensely yet 

 not fixedly developed, as shown by their extreme varia- 

 bility in the same species, and by their extreme diversity 

 in closely allied species, is that they have been acquired 

 as ornaments." 



One fact connected with these horn -like projections 

 gives as clear evidence as could be desired, that the male 

 is more liable to modification in this respect than the 

 female. It sometimes happens that the horns are ab- 

 sent in the males of a species, but present in a number 

 of closely related species, and in such cases we must be- 

 lieve that the departure from the general rule is due to 

 the fact that the species in which they are absent Las 

 been recently modified. Now, in such forms the female 

 shows her close relationship to the typical, unmodified, 

 or ancestral form by the possession of rudimentary horns. 



Darwin says that it is a highly remarkable fact that, 

 although the males of Onitis furcifcr do not exhibit 

 even a trace of horns on the upper surface of the body, 

 yot in the females a rudiment of a single horn on the 

 head and of a crest on the thorax are plainly visible. 

 The fact that the female of Bubas bison, a form which 

 comes next to Onitis, has a similar slight crest on the 

 thorax, while the male has, in the same situation, a 

 great projection, indicates, according to Darwin, that 

 the slight thoracic crest in the female Onitis is a rudi- 

 ment of a projection proper to the male, although it is 

 entirely absent in the male of this particular species. 

 The males of the genus Onitis give farther evidence of 

 plasticity, as they have not only lost the horns on the 

 upper surface of the body, but have also acquired new 

 and peculiar ones on the anterior pair of legs, and on 



