THE SEX RATIO IN HYBRID RA 1 - I(>7 



proportion of thi - amon- wild \..r\va\ -rat-. JtnL , >ni 



ill- ;tio found in general among the mammal-, it i- very 



probable ih.it there i- approximately an equality of th- 



in the wild Norway rat as in the albino rat. In the total of 



albino rai s i-\amined by Ciu'-noi and by myself there \va- found a 



ratio of io(). 40 mal.- to i oo female- Thi- -ex ratio i- con-id- 



'. throughout thi- |ia])cr. to expre-s the probable normal n-la- 



tion between th( \\ ild rat a- well a- in tin- albino rat. 



I "in series of experiments \\i-n- m.nle in which albino rat- 



\\ei ised \\ith \\ild Norway ; - R ( rds an- a\ ailable 



l"i d of \i,$ individuals belon^ini; to tin- 1 ^ciu-ralion. 



ot \\hich .so \\rn- in...' d 74 \\.-iv h-malr-. Amon- tlu-c 



lubrid-, ili: t sex i [20.26 males to too 



I male-. Although i hi- -. o is murh hi.chrr than that \\ Inch 



i- probabK normal |o- r of tl). nt -prcir-. il i- nol 



hiwl) .1- that t'-imd in \oii i . . m-ral ion of h> brid 



mil \\ hen- t In in the ratio . male- to loo 



Irlllalf- l.lblr I 



All ot tin- h\bi'd i g to thi I g< iii-raljon f ( .r \\hich 



irds were made wen . months old when the) \>. 



killed and examined; tin- leu indisidiial- lh.it died be!. :<'h- 



malmitN \\eie iioi iiu luded in il id-. li cannoi be 



deleiniined uith aii\ . to \\hal 



propi,rii,,n ol the < n:n, numbei prin^ brl. to tin I , 



generation the abo> o applie-. \.i\ t. \\ of the young 



rat- died, as i- kiio\\M, and there i- il" reason to -up; 



t hat l he mm talit \ \\ .1 n( it.-iii.tle- t h.in 



amour tin- ymir^ male-. It seems probable, then-fore, that the 

 -ex ratio in the l<>, indixidual- for \\hich data an- a\ailable i- 

 lairlx repiv-entati\e lor iln t ntire number of oiNprin^ produced 



in ihe coir the variou riments to which the) b-loir^eil. 



I WO Ol the lour -erii llllellt- Illelltiolled ,lbo\e U ere 



exteiidi d b\ mating \aiiou- individuals belong iir^ to the lir-t 

 lieiieration o| lubrid-. In pairing ihe-e animal- no attention 

 ua- paid to their blood relationship, and imdoiibtedK nearly 

 relati-d indixidual- \\ere mated in in. my cases. 



In "in- series "f experiment- only a \er\ -mall number of 

 indixiilual- beloiisjn- to the -econd generation of lubrid- died 



