1900.J MUS SYLVATICUS AND ITS ALLIES. 393 



speaking, be regarded as true, although now naturally modified by 

 recent accessions of material, so that I am able to distinguish 

 local forms, for the proper differentiation of which, although I 

 believe them to be perfectly recognizable and distinct, there was 

 needed the accumulation of a considerable number of specimens. 



Mus sylvaticus appears in fact to be a form which, in its longstand- 

 ing and successful struggle for existence, has attained to a height of 

 specialization from which it has either very little power of variation, 

 or else which is such as to fulfil all the needs of the species iu 

 almost any conditions with which it may be brought into contact. 

 The possible range of its variations, whether individual or geo- 

 graphical, would seem to be narrow. Within this narrow range, 

 however, variation is very evident and perplexing. The animal, 

 indeed, while apparently having small power of varying, uses to 

 the utmost the power which it possesses. Unlike some of our 

 common mammals, such as the Squirrel, Rabbit, or Eat, it is not 

 subject to either melanism or albinism. In the whole series of 

 the ' Zoologist ' and the volumes of the ' Field 5 for the last twenty 

 years, there is not to be found a single recorded instance of a well- 

 marked sport of this species — a result which would have been very 

 widely different had the object of the search been Sciurus vul- 

 garis, Talpa europcea, or Mus muscidus. This, of course, does not 

 prove that conspicuous sports do not occur, but it undoubtedly 

 emphasizes their rarity \ I have not thought it worth while to 

 supplement this result by a search for information, all of which 

 would probably be of a highly negative character, through any 

 number of the works of foreign writers; but neither in those of 

 Bell 2 nor of J. H. Elasius 3 can any allusion to such sports be 

 found. Dehne 4 , however, mentions a variety, which he calls " die 

 isabellfarbige Waldmaus," and which he characterizes as very rare, 

 since he had only seen one example, and that in the summer 

 of 1833 in the district of Penig. He had never seen white or 

 otherwise coloured varieties. De Selys-Longchamps a records an 

 " Isabelle albine" variety with pink eyes, and states that such 

 occur " tres accidentellement." Similar isabelliue, white, or white- 

 speckled varieties are noted as of extremely accidental occurrence 

 by Bonaparte 6 , Fischer 7 , and Mina Palumbo 8 . Mus sylvaticus is 

 then, it seems, a good instance iu support of Mr. A. Sedgwick's 

 remarks 9 on the loss of variability in au old species. 



1 It must not be forgotten also that sports of Mus sylvaticus may have been 

 occasionally credited to Mus muscidus. 



2 'British Quadrupeds,' ed. 2 (1874). 



3 'Saugethiere Deutschlands,' 1857. 



4 Aljgetn. deut. naturh. Zeit. 1858, pp. 182-3. 



5 ' Etudes de Micromaiumalogie,' 1839, p. 65. 



G ' Fauna Italica/ 1832-1841, art. on Mus sylvaticus. 



7 " Saugethiere des St. Petersburger Orouvernenients," Der Zoologische Garten 

 18G9, p. 340. 



8 Oat. dei Mainm. della Sicilia, 1808, p. 72. See E. Cantoui's " Elenco Qenerale 

 dei Maininiferi soggetti ad albinisuio," in Atti della Sue. Ital. di Sci. Nat. 

 vol. xxiii., 1880. 



s Presidential Address to Section D of British Association : Dover, 1899. 



