318 LAWS OF VARIATION. Chap. XXV. 



in correlation with, the elongated and reversed feathers on the 



back of the neck, which form the hood. 



The hoofs and hair are homologous appendages; and a 

 careful observer, namely Azara, 11 states that in Paraguay 

 horses of various colours are often born with their hair curled 

 and twisted like that on the head of a negro. This peculiarity 

 is strongly inherited. But what is remarkable is that the 

 hoofs of these horses " are absolutely like those of a mule." 

 The hair also of their manes and tails is invariably much 

 shorter than usual, being only from four to twelve inches in 

 length ; so that curliness and shortness of the hair are here, 

 as with the negro, apparently correlated. 



With respect to the horns of sheep, Youatt 12 remarks that 

 " multiplicity of horns is not found in any breed of much value ; 

 " it is generally accompanied by great length and coarseness 

 " of the fleece." Several tropical breeds of sheep which are 

 clothed with hair instead of wool, have horns almost like 

 those of a goat. Sturm 13 expressly declares that in different 

 races the more the wool is curled the more the- horns are 

 spirally twisted. We have seen in the third chapter, where 

 other analogous facts have been given, that the parent of the 

 Mauchamp breed, so famous for its fleece, had peculiarly 

 shaped horns. The inhabitants of Angora assert 14 that " only 

 ' ; the white goats which have horns wear the fleece in the 

 " long curly locks that are so much admired; those which 

 " are not horned having a comparatively close coat." From 

 these cases we may infer that the hair or wool and the horns 

 tend to vary in a correlated manner. 15 Those who have tried 

 hydropathy are aware that the frequent application of cold 

 water stimulates the skin ; and whatever stimulates the skin 



11 ' Quadrupedes du Paraguay,' apt to vary together." Dr. Wilckens 

 torn. ii. p. 333. ("Darwin's Theorie," 'Jahibuch 



12 On Sheep, p. 142. der Deutschen Viehzucht,' 1836, 1. 



13 ' L'eber Racen, Kreuzungen." &c, Heft) translates my words into " lang- 

 L8'25, s. "-'-4. und grobhaarige Thiere sollen ge- 



14 Quoted from Conolly. in 'The neigter sein, iange und viele Horner 

 Indian Field/ Feb. 1859, vol. ii. p. zu bekommen," and he then justly 

 266. disputes this proposition; but what I 



15 In the third chapter I have said have really said, in accordance with 

 that " the hair and horns are so Uose- the authorities just quoted, may, ] 

 ly related to each other, that they arc think, be trusted. 



