Chap. Ill 



THEIR VARIATION. 



79 



drical, about three inches in length, covered with bristles, 

 and with a pencil of bristles rising out of a sinus on one 

 side : they have a cartilaginous centre, with two small longi- 

 tudinal muscles: they occur either symmetrically on both 

 sides of the face or on one side alone. Eichardson figures 

 them on the gaunt old " Irish Greyhound pig ; " and Nathu- 

 sius states that they occasionally appear in all the long eared 



Fig. 4.— Oid Irish Pig, with jaw-appendages. (Copied from H. D. Richardson on Pigs.) 



races, but are not strictly inherited, for they occur or fail in 

 animals of the same litter. 25 As no wild pigs are known tc 

 have analogous appendages, we have at present no reason to 

 suppose that their appearance is due to reversion ; and if 

 this be so, we are forced to admit that a somewhat com- 

 plex, though apparently useless, structure may be suddenly 

 developed without the aid of selection. 



It is a remarkable fact that the boars of all domesticated 

 breeds have much shorter tusks than wild boars. Many facts 

 show that with many animals the state of the hair is much 

 affected by exposure to, or protection from, climate ; and as 

 we see that the state of the hair and teeth are correlated in 

 Turkish dogs (other analogous facts will be hereafter given), 

 may we not venture to surmise that the reduction of the tusks 



25 Eudes Deslongchamps, 'Me - * Pigs, their Origin, &c,' 1847, p. 30 

 moires de la Soe. Linn, de Normandie,* Nathusius, ' Die Kacen des Schweines,' 

 vol. vii., 1842, p. 41. Richardson, 1863, °. 54. 



