262 C. E. Beechsr — Origin and Significance of Spines. 



originally, varieties are found without horns, and others with 

 horns, showing all degrees of twisting and length. 



By protecting cattle from enemies, by forcing them into 

 changed environment, and by varying amounts of nutrition, 

 man has evidently brought the original stock into a condition 

 of free variation. This state has been made use of in the pro- 

 duction of endless varieties by selection and cross-breeding. 



Darwin 14 accounts for the sexual selection affecting the 

 growth of the antlers in the Deer as due to excess in the num- 

 ber of male individuals, and their struggles for supremacy in 

 the possession of a mate. The antlers at the breeding season 

 are strong and solid, and are therefore at their maximum of 

 efficiency in each individual. They are shed at or before the 

 time the young are born. Previous to the growth and maturity 

 of the new antlers, the young are so far advanced as to be able 

 to avoid being killed by the adult males. Furthermore, 

 Darwin suggests that the excessive development of antlers 

 into palmate and arborescent forms was probably an orna- 

 mental character attractive to the females. These complicated 

 antlers not being the most efficient weapons, the fighting pro- 

 clivities of the males would tend to favor the individuals with 

 simple antlers, and to repress the more differentiated forms. 

 Thus, the two influences would be opposed to each other, 

 though not necessarily equal. The law of the multiplication 

 of effects may also have some force, since it may carry a struc- 

 ture beyond the bounds of efficiency. Even in one of the 

 oldest horned mammals, the P rotocerus*' 3 of the Miocene Ter- 

 tiary, a great difference is seen in the horns of the two sexes. 

 The female has little nodes or tubercles, which in the male 

 rise to the height and prominence of the horns on the Giraffe, 

 or are even relatively more pronounced. 



The males of some other vertebrates have spiniform processes 

 or spurs on their legs and wings serving particular functions. 

 The spurs in birds are to be considered mainly as weapons 

 which are used by the males in combats among themselves. 

 They are developed on the metatarsal or metacarpal bones as 

 bony processes ensheathed in horn. In the females, the spurs 

 are generally rudimentary. A kind of spur is also found on 

 the hind limbs of the male Echidna and rnithorhynchus^ 

 attached to the astragalus. It is perforated by a duct lead- 

 ing from a gland. The functions of the spur and of the 

 secretion are unknown. 



Many lizards especially among the Chameleons present 

 striking differences between the sexes, and the males of some 

 of them develop veritable horns like those- in cattle, sheep, 

 and other hollow-horned ruminants. Darwin 14 illustrates and 

 describes a number of most interesting examples. One of 



