590 



THE DESCENT OF MAN 



shown by their extreme variability in the same species, 

 and by their extreme diversity in closely allied species. 

 This view will at first appear extremely improbable; but 

 we shall hereafter find with many animals standing much 

 higher in the scale, namely, fishes, amphibians, reptiles, 

 and birds, that various kinds of crests, knobs, horns, and 

 combs have been developed apparently for 

 this sole purpose. 



The males of Onitis furcifer (Fig. 21) 

 and of some other species of the genus are 

 furnished with singular projections on their 

 anterior femora, and with a great fork or 

 pair "of horns on the lower surface of the 

 thorax. Judging from other insects, -these 

 may aid the male in clinging to the female. 

 Although the males have not even a trace 

 of a horn on the upper surface of the body, yet the females 

 plainly exhibit a rudiment of a single horn on the head 

 (Fig. 22, a), and of a crest (6) on the thorax. That the 

 slight thoracic crest in the female is a rudiment of a projec 



Fio. 31.— Onitis furci- 



fer, male, viewed 



from beneath. 



Fio. 22.— Left-hand figure, male of Onitis furcifer, viewed laterally. Eight-hand 

 figure, female, a. Rudiment of cephalic horn. 6. Trace of thoracic horn or crest. 



tion proper to the male, though entirely absent in the male 

 of this particular species, is clear; for the female of Buhas 

 bison (a genus which comes next to Onitis) has a similar 

 slight crest on the thorax, and the male bears a great pro- 

 jection in the same situation. So, again, there can hardly 

 be a doubt that the little point (a) on the head of the female 

 Onitis furcifer, as well as on'the head of the females of two 

 or three allied species, is a rudimentary representative of the 



