i^iVl MIL .(. LEWIS H()\II(»TE O.N THE [^Pl"- ^ 9» 



iiii'uiis of iiuliviiliiiiUy (li.stiii<,'iii.sliiii<r iIr- diHerent fonus or muta- 

 tions, a.s we may now, I think, call them. 



Here, therefore, in an entirely difierent species we tind the 

 same mutations present, and wliereas in the case of the one 

 (J/, raltios) we are enabled to distinufuish easily the various forms 

 owing to the combimitiou of tlie hind-foot character with a colour 

 character, yet in the other species (J/, iiorveyicas) we are unable 

 to subdivide it into three forms, owing to the impossibility of 

 detinitely detecting which character is present in any particular 

 indixidual. Nevertheless we have cognisance of characters 

 (mutations) which cannot be recognised by any external inspec- 

 tion of individuals, although we have proved their presence 

 beyond a doubt. 



It wouhl of course be rash to l)e too positive, yet it is ex- 

 tremely unlikely that tliese rats cend in any way to pair accoi'ding 

 to their foot charncter. If the characters were therefore merely 

 individual variations, the)' would undoubtedly tend to be swamped 

 and an even curve would result. This, however, is not the case. 

 [For purposes of comparison we liave added (Table V., text- 

 tig. G2) a curve of the hind foot of Acomys caliirinus ; this, it 

 will be noted, is a perfectly simple curve with only one apex. 

 As the number of Acomys measured (about 100) was nearly the 

 same as the number of M. alexandrinus, the comparison is a 

 perfectly fair one.] 



We have here, therefore, in M. nnrvpyicus a splendid example 

 of a Mendelian character (mutation) being carried on unimpaired 

 through generations ; and there can be little doubt that if tliese 

 animals found themselves under certiiin conditions whei'e small 

 feet, for example, jjrove of great advant^vge, very few generations 

 would suffice for the small-footed race to become the dominant 

 form. 



The Mendelian theory enal)les us to understand how a. small- 

 footed race could he produced in a very short time, or how, if that 

 favourable mutation were not present, the species might die out 

 before the cumulative efleots of Natural Selection on continuous 

 variation would have tiine to act. 



(J'ineral Notes. 



iVIuch work of value still remains to be done by encjuiry into 

 tlie gradual formation of species, and tluse rats uHei- a wide field 

 for the study of minute variations. Many groups of the smaller 

 loilents as, for example, rats of the Mi<s jirdoni grouj) and many 

 of the (,)riental groups of .S(juiri-els, otter similar pioblems of great 

 complexity. In the former case we ha\e nund)ers of very closely 

 allied foinis all inhabiting the same district, and each form has, 

 appaiently, its representative in other neighbouring districts. 

 Systematists of late years have been content to buiden each of 

 these forms with a different name Mud tlu-re to \v:\\v the matter. 

 Such \\(ii-k, necessary a.s it may lie. can lie Imt ,i preliminary 

 step, and indess the subject is purslied further, the chaos 



