54 STUDIES IN EVOLUTION 



Marsh suggests to the writer that these variations in the 

 directions of the horns have been influenced by the climate. 

 A warm climate permits the horns to stand out directly from 

 the skull. Further north, or in a colder region, the frequent 

 freezing of the horns and their consequent drooping has 

 induced a natural drooping condition, and an Arctic climate 

 has resulted in the production of horns closely appressed to 

 the skull, in which position they cannot be affected by freez- 

 ing temperatures. 



Another possible service for antlers is also suggested by 

 Marsh. As is well known, the male Moose is one of the 

 most wary of the Cervidse, and detects noises at great dis- 

 tances. The large palmate antlers act as sounding-boards, 

 and, when listening, the animal holds his ears in the focus of 

 the anterior surfaces of the antlers. 



The hollow-horned mammals afford some of the most evi- 

 dent examples of the use of horns for protection and offence. 

 In species with permanent horns, like the bison, oxen, goats, 

 cattle, antelopes, etc., the horns are generally present in both 

 sexes, though in the males they are often much the larger. 

 In defence, many of the horned ruminants hold the head 

 down, thus protecting the nose and bringing the top of the 

 skull into prominence. In this position the horns are most 

 effective. A similar posture is taken by the horned batra- 

 chians and lizards. 



The Porcupine and Echidna rely largely on the protection 

 afforded by their spines, and on this account they are sluggish 

 in their movements, and make little effort to escape approach- 

 ing enemies. 



Many of the great horned Dinosauria of the Mesozoic are 

 well provided with an armature of protective plates and spines 

 on various parts of the body. In addition to an armature on 

 the body Triceratops^^ had three large horns on the head, 

 one median (nasal) and two lateral (supra-orbital). These 

 were powerful offensive and defensive weapons. There were 

 also other small nodes and spiniform ossicles around the 

 posterior crest of the skull and on the jugals, forming a part 



