THE ARCHIPELAGO OP BREHAT. 89 



or an island, correspond with the extent of land ap- 

 propriated to them, so that they diminish in number 

 and size in proportion to the diminution of the ha- 

 bitable space around them. This proposition is true 

 with regard to the case in point. We find at Brehat 

 all the species of mammals, birds and reptiles be- 

 longing to Chausey, while each of these classes is 

 represented by several additional forms ; in the first 

 division, we have the ermine and polecat, in the 

 second the linnet and blackbird, and in the third the 

 common adder and the newt. The aquatic birds 

 seem, however, to present an exception to the rule, 

 for there are fewer species than at Chausey, and 

 those which are met with are of a smaller size ; this 

 apparent contradiction may, however, be explained 

 by the fact that the channels of Brehat are not so 

 well stocked with fish as those in the Chausey ar- 

 chipelago, and that consequently there is nothing to 

 attract these birds, which, moreover, are distinguished 

 by their wandering habits from the true representa- 

 tives of the native fauna. 



It is worthy of notice that the Mammals of Brehat 

 number amongst their representatives two species 

 of the genus Mus, namely, the mouse and the black 

 rat. The black rat, which has become more and 

 more rare, is disappearing daily from the continent of 

 Europe in consequence of a revolution, not less 

 bloody, though less generally known than those which 

 the barbarians of the north brought in former times 

 upon the empires of the more civilised world. For 

 ages, the mouse, which was the only representative 

 of this family known to the ancients, lived at our ex- 



