CONCLUSION. 



17 



assign some meaning to urax ; and the fact that some lexicographer* 

 give rat as its equivalent, leads me to be very willing to pick up an 

 unoccupied name, the adoption of which cannot lead to any con- 

 fusion with other species. It may be safely said of this uracoid 

 mouse that if it had originated apart, and if 1 had not had perfect 

 proof of its descent, there would have been plenty of speculation as 

 to its being probably a hybrid, with some allied species of 3Ius, and 

 its discovery might have marked the epoch of a controversy as dire 

 as that which attended the 'leporine.' I am not, however, tempted 

 to place this accidental variety on a higher pedestal than that which 

 its singular appearance most certainly merits. The variation which 

 has led to so many colours being produced from one blood is really 

 due to the law which M. De Selys-Longchamps, and later Mr. 

 Charles Darwin, have insisted on, that the offspring do not neces- 

 sarily partake of the colours of the parents, but revert according to 

 the law of ' atavism ' in some cases to the primitive ' wild ' type of 

 tlie Mus musculiis ; in others to imitate sister varieties in colours 

 that the parents did not themselves possess ; and in this case, to 

 return to a physiognomy which I may call, not especially the rat 

 type, but the generalised murine type. The excess of dark pigment 

 in the tail is a significant fact coupled with the entire paucity of its 

 existence in both parents and brethren. 



''Another example may be given in which the law of 'atavism' 

 does not go quite so far. Two white mice are paired, and there is a 

 progeny of seven. Four of these are indistinguishable from the wild 

 mouse of our houses, and three are white like the parents. Here the 

 preserved absence of plum-coloured, fawn-coloured, or black elements 

 in the parents of the white mice has not led to the progeny throwing 

 any of those varieties in colour which have produced piebald (or 

 rather skewbald) mice elsewhere in such profusion. The case ia 

 one, therefore, of simple reversion to the specific, not to the generic 

 type, and it has occurred exactly in the most aberrant variety, i.e., 

 the albino. 



" Darwin has well shown that when grey and white mice are paired, 

 the young ones are not piebald nor of an intermediate colour, but all 

 pure white or of the ordinary grey colour ; so it is when wisite and 

 common coloured turtle doves are paired. He takes this as an 

 example of the law that when two breeds are crossed, their characters 

 usually become intimately fused together, but some characters refuse 

 to blend, and are transmitted in an unmodified state, either from 

 both parents or from one. Mr. J. Douglas remarks, with regard to 

 game fowls, a strange fact that if a black and a white game are 

 crossed, the birds of both breeds are obtained of the clearest colour. 



" Analogous facts have been observed with plants. It is remark- 

 able, as has been strongly insisted on by Isidore Geoffroy St. Hilaire 

 in regard to animals, that the transmission of characters without 

 fusion occurs most rarely when species are crossed. Mr. Darwin 

 only knows of one exception, it being in the hybrids naturally pro- 

 duced between the common and hooded crow (0. cor one and comix) y 

 which, however, are closely allied species, differing in nothing except 



B 2 



