APPENDIX. 3. j 9 



tions." "The unquietude," says another author, "which they 

 manifest might in case of need serve as an almanack." " The 

 shepherds must then exert all their vigilance to prevent them 

 escaping," " for it is a known truth that they would go to the 

 very plait- where they had been born." Many cases have 

 occurred of three or four sheep having started and performed 

 the journey by themselves, though generally these wanderers 

 are destroyed by the wolves. It is very doubtful whether 

 these migratory sheep are aborigines of the country; and it 

 is certain that within a comparatively recent period their 

 migrations have been widely extended: this being the case, I 

 think there can hardly be a doubt that this "natural instinct," 

 as one author calls it, to migrate at one particular season in 

 one direction has been acquired during domestication, based 

 no doubt on that passionate desire to return to their birth- 

 place which, as we have seen, is common to many breeds of 

 sheep. The whole case seems to me strictly parallel to the 

 migrations of wild animals. 



Let us now consider how the more remarkable migrations 

 could possibly have originated. Take the case of a bird being 

 driven each year, by cold or want of food, slowly to travel 

 northward, as is the case with some birds; and in time we 

 may well believe that this compulsory travelling would 

 become an instinctive passion, as with the sheep in Spain. 

 Now (lining the long course of ages, let valleys become con- 

 vert, m! into estuaries, and then into wider ami wider arms of 

 the sea; and still I can well believe that the impulse which 

 leads the pinioned goose to scramble northward would lead 

 OUT bird over the trackless waters ; and that, by the aid of 

 the unknown power by which many animals (and savage 

 men) can retain a true course, it would safely cross the 

 sea now covering the submerged path of its ancient land 

 journey.' 



• I do ii"t rappoM that ill.- line of migration <>( birds always marks ilio 



lini' >>{ tot rlj continuous land. Ii is possible thai a bird accidentally 



blown to a distant land or island, after staying - e tune and breeding there, 



might I"- induced bj its innate instinct to flj away, and again to return there 



in tin- breeding s e ason. Hut I know of no mots to countenai the ideaj 



mid I hare been much struck in the case of oceanic islands, lying at bo bx« 



oessire distance from the mainland, but which Br vasons to be giren in a 



future chapter I <lo not beliere have erer been joined to tl"' mainland, irith 

 the i "i that thej seem moot rarelj to have any migratory birds, Mr. B \ . 

 Haroourt, who has written on tin' birds of Madeira, informs me thai then 

 an none in thai island) to, I am informed bj .Mr. Garew Hunt, a m in tin' 



