«66 



AGENCY OF MAN 



[Ch. XXXIX. 



West Zetland Islands ; "^ and, according to Sibbald^ ' the 

 same animal came into Orkney/ Another was taken, in 

 1774, in the Severn, according to Turton. Two instances 

 also, of the occurrence of the leathern tortoise (0. cormcea), on 

 the coast of Cornwall, in 1756, are mentioned by Borlase. 

 These animals of more southern seas can be considered only 

 as stragglers attracted to our shores during uncommonly warm 

 seasons by an abundant supply of food, or carried by the 

 Gulf-stream, or driven by storms to high latitudes. 



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Some of the smaller reptiles lay their eggs on aquatic 

 plants ; and these may often be borne rapidly by rivers, and 

 thus conveyed to distant regions. • ■ . 



But that even the larger ophidians may be transported 

 across the seas, is evident from the following most interesting 

 account of the arrival of one at the island of St. Vincent. It 

 is worthy of being recorded, says Mr. Guilding, ' that a noble 

 specimen of the Boa constrictor was lately conveyed to us 

 by the currents, twisted round the trunk of a large sound 

 cedar-tree, which had probably been washed out of the bank 

 by the floods of some great South- American river, while its 

 huge folds hung on the branches, as it waited for its prey. 

 The monster was fortunately destroyed after killing a few 

 sheep, and his skeleton now hangs before me in my study, put- 

 ting me in mind how much reason I might have had to fear 

 in my future rambles through the forests of St. Vincent, had 

 this formidable reptile been a pregnant female, and escaped 

 to a safe retreat.' f 



Involuntary agency of man in the dispersion of animals. — In a 

 future chapter I shall speak of the transportation by man to 

 distant regions of quadrupeds and birds which are useful to 

 him, and of the effect of such colonisation in limitinof the 

 range and sometimes extirpating indigenous species of plants 

 and animals. I shall merely consider in this place the invo- 

 luntary or unintentional aid which we frequently lend to the 

 dissemination of species, many of them not only unservicable 

 but noxious and injurious to us. 



Thus we have introduced the rat, which was not indigenous 



-^ Brit.'Animals, p. 149, wlio cites Sibbald. 

 t Zool. Journ. vol. iii. p. 40G. Dec. 1827. 







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