604 Ml!. J. l::wis lioNiioTK ox the [-^P^"- 1^> 



le;ist, <rivon ;\ woikiiiij liyjiotlu'sis on wliicli we iii:iy atteiupt to 

 solve .siiiiic dt" (lie piolilcnis of licredilv ; inul tlioiigh 1 am far 

 from adiiiittiiig tliiifc Meiulel's law is the sole, ov even the chief, 

 f.-ii'toi- <(oveinin^ heieility, it does undoubtedly help us to under- 

 stand Jiow these closely allied forms can either (i.) exist in tl)e 

 san\e locality as distinct varieties, or (ii.) in another locality 

 l)rc()me apparently lost althou^^h a closer inspection sliows them to 

 lie present, only waiting for a suitable environment in wdiich to 

 de\elope. 



To prove tin's matter furtiiei-, it lu'comes necessary to conduct 

 Mendelian experiments on these varieties. This I have begun to 

 do on a, small scale. The experiments are, however, as yet in the 

 iiiili;il stages and no definite results can be stated. So far as 

 they have gone, we find that pure J/, tectorrovi mated with pure 

 J/, tectonciii have jjroduced pure j\I. teciofion. Pui'e J/, alexau- 

 drhias when paired together have also bred absolutely true. A 

 })air of grey M. iectoruvi (group ii.) showing slight traces of brown 

 on the feet ])roduced young like themselves (group ii.) and grey 

 M . (ilex(imlri)n(s (group iii.). 



As far as it goes, therefoi'e, this evidence seems to further 

 confirm the fact tliat Mas rattiis should not be regarded as 

 i\ species in which variation has inii w ild, I)ut i-ather as a spt^cies 

 containing cei'tain definite nuitatitjus, which when mated together 

 breed perfectly true. From its wandering habits and prolific 

 breading much intercrossing takes jilace, giving rise to these 

 innumerable varieties, hut no lieltci- evidence could be had of the 

 purity of the gametes than the f.ict that when the apparently 

 I line laces ai-e mated together (even when captured amongst a 

 niixeil crowd) they breed absolutely true. 



tS' II jiiiii (()•)/. 



'i"he main points that have l)een brought out in this paper are 

 as follows : — 



(i.) Two \arirties (and iiit ( rnicdiates) of J/, /-((tins -.wv found in 



(ii.) The himl Too*, is taken as a standard nicasurcnient and 

 curves of this nieasin'enicnt. draw n. 



(iii.) These cnrNcs show three apices, the liist being very 

 small. 



(i\.) These 1hiei> apices correspond with tla^ length of the 

 hind foot tyjiical of the three subgroups of J/, rattus in the 

 (•liental Region (h'scribed by myself some years ago, 



(v.) Hence it is argued thnttliese tlnee apices proliably repre- 

 sent mntatioitf!, and that the first and smallest apex represents 

 the ./(dnrensin subgroup found in the Oriental Region, but which 

 from some cause or other is practically non-existent in Egvi>t. 



Since. lio\\e\er. a iii ii/a t I'lui cannot be (lest roxcd, w(^ still 

 lind it in a .■-mall )ieiceiitage I'l i ml i\ idiial.- ready under favour- 

 alile cin'Uin>lances (o imava-se. 



