278 MAMMALS. 



mentions that the island was frequented about 150 j'cars since by vessels belonging to the 

 buccaneers : this therefore gives the date, and he adds, " If a peculiar climate, volcanic soil, and 

 strange food, can together produce a race or strongly marked variety, there is every probability of 

 such change having taken place in this case."* 



The Egyptian Rat (Mus tectorum, or Mus Alexandiunus) is another species which may possibly 

 have been an offshoot from, or descendant of, the Brown Rat (Mus decumanus). The former is now 

 common in Italj', where it must have come apparently about the same time as the other ; for, as 

 already said, Rats were unknown to the ancient Romans. It comes nearer the Brown Rat than the 

 Black Rat, although, like it, it has the tail as long as the head and body together, which the Brown 

 Rat has not. Its habits differ somewhat from those of the latter, preferring dry places — a point on 

 which the Brown Rat is indifferent. 



There is another fact which may be used as an argument both for and against its being 

 a scion of the Brown Rat, and that is, that the two are at all times in a state of determined hostility ; 

 but being stronger and more courageous than the Black Rat, the Egj'ptian species has been able to 

 wage a more equal warfiu-e with the former, and has hitherto escaped extermination. Their mutual 

 antipathy may be an argument against their common parentage — although family quarrels are 

 usually said to be the most bitter — and their strength and courage ma)^ be pointed to as qualities 

 which it might be likely to possess if descended from the Brown Rat. If we coidd argue from our 

 present knowledge of the Brown Rat's constitution, viz. that it bears all climates, and only varies 

 when protected by isolation from the restoring influence of fresh blood of the common stock, that 

 would dispose of the question without the necessity of goiag into these topics ; but the fact is, that we 

 know its history for such an infinitesimal portion of time — not a couple of hundred years — that we 

 cannot tell whether it is less or more liable to change than any other animal. If the Mus tectorum 

 is descended from the Brown Rat, it has passed the phase of variety, and become a full species. 



Again, on the Island of Ascension, Mr. Darwin foimd two Rats, — varieties, as he and Mr. 

 Waterhouse consider, of the Black Rat. These two animals differ in the colour of the fur, one 

 being of a grizzled brownish colour, the other black, with more soft or glossy fur. That which has 

 a black and glossy fur frequents the short, coarse grass near the summit of the island, where the 

 common Mouse likewise occurs. It is often seen running about by day, and was found in numbers 

 when the island was first colonized by the English. 



The other, and browner-coloured variety, lives in the outhoiises near the sea-beach, and feeds 

 chiefly on the offal of the turtles slaughtered for the daily food of the inhabitants. " If the settle- 

 ment were destroyed," says Mr. Darwin, " I feel no doubt that this latter variety would be com- 

 pelled to migrate from the coast. Did it originally descend from the summit ? and in the case first 

 supposed, would it retreat there ? and if so, would its black colour return ? It must, however, be 

 observed that the two localities are separated from each other by a sjiace some miles in width, of 

 bare lava and ashes. Does the summit of Ascension, an island so immensely remote from any 

 contraent, and the summit itseK surrounded by a broad fringe of desert volcanic soil, possess a small 

 quadruped peculiar to itself? or more probably, has this new species been brought by some ship 

 from some unknown quarter of the "World ? Or I am again tempted to ask, as I did in the case of 

 the Galapagos Rat, has the common English species been changed by its new habitation into a 

 strongly marked variety ?" t Mr. Waterhouse remarks upon this: " It appears as if the brown and 



* Darwin in " Zoology of the Beagle," part ii. Mammalia, p. 35. 

 t Darwin, loc. cit. 



