THE METHOD OF CREATION OF ORGANIC FORMS. 199 



Espada, to be developed into short horns. That this excessive 

 ossification is associated with the habit of protecting the whole 

 body with the front seems likely. 



In the case of Phrynosoma we know that precisely the same 

 habit is associated with the presence of the sharp horns ; and that 

 some genera without horns possess it also. Phrynosoma is an ex- 

 ceptionally sluggish genus in a family of most active forms, and 

 must necessarily resort to this mode of defense more than they. 



In the case of Euminants, we also know that defense is accom- 

 plished by throwing the head down with the horns thrown for- 

 ward. But this is not confined to this group. That generalized 

 suborder, the Artiodactyla Omnivora, represented by the hog, 

 which were no doubt the genetic predecessors of the Euminants 

 in time, also throw the head down in defense in the same way, 

 having thus a manner totally distinct from that seen in the Car- 

 nivor'a. The latter show their teeth and often crouch j^repara- 

 tory to a leap. 



These cases present so constant an association between habit 

 and use that, admitting evolution, we are compelled to believe 

 that the structure has given rise to the habit or the habit to the 

 structure. In the former case we have to suppose, with the au- 

 thor of "Natural Selection," that among the many spontaneous 

 variations rudimental horns occasionally appeared, and that their 

 possessors, being thus favored in the struggle for existence, were 

 preserved and multiplied ; while those not favored dwindled, and 

 were ultimately nearly all extirpated or starved. The question 

 of origin is here left to chance, and Alfred Bennett has made a 

 mathematical estimate of the chances of any particular profitable 

 variation occurring among the great number of possibilities of the 

 case. This has shown the chance to be so excessively small as to 

 amount in most cases to a great improbability. 



If we turn to the probabilities of such structure having arisen 

 through the selection of that mode of defense by the animal, we 

 find them greatly increased. The position occupied by the horns, 

 in all the animals described, is that which is at once brought into 

 contact with an enemy in conflict, and as sport among animals is 

 a gentle imitation of conflict, the part would be constantly excited 

 in sport as well. With an excess of growth-nutrition, our knowl- 

 edge O'f the effects of friction on the epidermisj and of excessive 

 ligamentous strain and inflammation on bone (e. g., spavin in 

 horses), as well as of abnormal exostoses in general, would warrant 



