THE SEX RATIO IN HYBRID RATS. IOQ 



tin- other individuals belonging to the F? generation, a- \\e! : 

 those for the hybrid- of the F 3 generation. -ho\v an excess of 

 female-. The-e latter record-, cannot be considered to turni-h 



lence against Dti-in:;'- theory, since they include -uch a 

 very -mail number of individual-. There seem to be no record-, 



pt th' en by I Hi-ing, that -ho\v that inbreeding alone 



prodni e- a relaii\eh . r number of male than ot temale 



offspril . - liull/<- \\a- unable to de!r. t any change in the 



rat io <if albino mice that had been inbred for four generation-, 

 and I have found no unu-ual !' male- anioii- some 500 



individual- beloii^in^ io ti\e generations of inbred albino rat-, 

 keeoid- are available for ui other hybrid rat-, nio-t ot uhii'h 

 \\ere ihe oti-prin^ "f reciprocal Cl I'he-e indixidiial- all 



belonged to the I _ or to the I ^-neralion of hybrid-; and amon- 

 them were 7- male- and 4<i tVnul. 5. Thr-e In brid- \\ ere -elect .d . 

 b-< au-e of their -i/e and condition, from a considerable number ot 

 indi\ iilual- for \\liich im record- \\eiv made. There \va-. theie- 

 fore, lindoiibtedK all lllicoll-cii -U- -. leetjoii of male- in choo-in- 

 the rat- to be , \amined. -inv the adult male rat i- considerably 

 larger and hea\ ier than the female. The data for the-e Nation- 

 lot- of -(lei ted indi\idual- ha\e been coinbine<l in one ;;ioiip, 

 -iiii-e the\ are of \.ilm- onl\ 1 -ho\\ the -e\ o| a 



( on-iderable number -.1 h\ bi id-. 



The |o|lo\\ iii'^ table ;J\e- i -imim.HA of the 5CX record- |o|- 

 all ot t he h\ briil rat- te. . nded. 



TABU II. 



llshkli' 1< 



In the total of 425 lubiid rat- lor \vhich ri'cord- \\ere made, 

 j;i \\eiemale-and I i \ \\ el e lelliale-. .\mon.uthe-eilldi\idual-, 

 therefore, there i- found a -e\ ratio \\hieh i- con-ider.ibl\ higher 

 than that \\hich i- probably normal for either the albino or the 

 \\ild \oi\\a\ rat, -ince there are \\<>.<) male- to loo female-. 



