744 



THE NATURE BOOK 



existence between the two species, which 

 is actually in progress, at the present 

 moment, both in Europe and America. 

 Its progress in the past has been marked 

 in many localities, including the British 

 Isles, by the practical annihilation of the 

 unfittest. Apart from the disparity of 

 strength between Rat and Ratton, the 

 prominence of the latter's eyes and ears 

 are a decided handicap to him in battle, 

 and it must also be remembered that the 

 " weeding out " process, which naturally 

 accompanies migration, ensured that the 

 Rattons should be attacked in the first 

 instance by a race of hardy campaigners. 



The coloration of the Common Brown 

 Rat hardly needs description. There 

 is generally a sharp differentiation be- 

 tween the grey brown of his back and 

 the white of his belly, and his body fur 

 is decidedly coarse. In the Brown Ratton 

 we find the same colour scheme pre- 

 dominant, though the fur is of much finer 

 texture. In the Blue and Black Rattons 

 the body pelage presents a peculiar 

 metallic sheen, typically bluish in the 

 Blue Ratton and typically greenish in 

 the Black, while the colour of their belUes 

 differs but shghtly from that of the sides 

 and upper portions of their bodies. 



The history of Rats and Rattons is 

 of great interest. It is certain that Rattons 

 of some kind inhabited Europe before the 

 dawn of history. Remains of the species 

 have been found in West German pile 

 dwellings, and also in Italy, under cir- 

 cumstances which leave no reasonable 

 doubt as to their antiquity. The Brown 

 Ratton first attracted attention during 

 Bonaparte's occupation of Egypt, and 

 was named the Alexandrine Rat by 

 Geoffroy. Until the investigations of 

 De ITsle in 1865 proved that it was 

 impossible to separate him anatomically 

 from the Blue or Black Rattons, he 

 was regarded as a chstinct species. De 

 ITsle advanced the theory that the Brown 

 Ratton was the primitive type. An 

 interesting series of breeding experiments 

 showed him that the mating of a Black 

 male Ratton with a Brown female pro- 

 duced generally an all-black htter, while 

 the mating of a Brown male with a Black 

 female ])roduced generally a mixed litter 

 in which the darker tint predominated. 

 He further suggested that there was a 



tendency in parasitic animals of the genus 

 Mus to become uniformly dusky in tint 

 and to lose the dark upper-, hght under- 

 coloration, which is characteristic of so 

 many wild creatures, and which is held 

 to be protective by reason of the hght 

 portions being normally in shadow. 



On these grounds he held that the origi- 

 nal out-of-doors Ratton was brown above 

 and white below, this being the combina- 

 tion which best suited his normal environ- 

 ment, and that the all-over duskiness of 

 the prevalent European type was an 

 adaptation to indoor surroundings. De 

 ITsle's theory held its ground for a 

 generation, but it was disputed by Forsyth 

 Major, and it is the latter's view which 

 is now generally preferred. This view 

 is based on the palasontological aspect 

 of the case. It is an observed fact that 

 highland species tend to be darker in 

 colour than lowland species. In cases 

 where a single species includes both 

 highland and lowland varieties the ten- 

 dency to melanism in the former is marked. 

 It has been observed in the common 

 squirrel, in bats, in meadow mice, and 

 in several species of reptiles and amphi- 

 bians. If we admit that colour variation 

 is chiefly a matter of climate, and assume, 

 as we are almost certainly justified in 

 assuming, that the chmate of N.E. Africa 

 and Arabia in the Quaternary Epoch 

 was similar to that of modern Europe, the 

 probabihty of the original immigrant 

 Ratton having been as dusky as his 

 modern mid-European descendants be- 

 comes an extremely strong one, and the 

 evolution of the Brown Ratton from the 

 primitive black type must be attributed 

 to the gradual climatic change which 

 turned the quaternary moors into sandy 

 deserts. 



The incursion of the Brown Rat into- 

 Europe occurred less than two hundred 

 years ago, but we know nothing of the 

 causes which impelled him to cross 

 the Volga, nor have we any certain know- 

 ledge as to whence, or why, he came. It 

 is practically certain that he did not come 

 from India, where Rattons abound, and 

 it is likely that his original home was 

 considerably further to the East. 



His passage of the Volga, which was 

 to be fraught with such grim meaning 

 for the European Rattons, occurred. 



