THE SEX RATIO IN HYBRID RATS. IO5 



In order to -tudy the color combinations in hybrid mice von 

 (.uaita ('98, 'ooj crossed albino mice with Japaiu-e waltzing 

 mice and inbred their descendants through six generation-. In 

 hi- various table- von ' '.uaita gives the sex of the great majority 

 of the hybrid oiT-prin- obtained in each generation, yet he maki - 

 no comment whate\er "ii tin- relative proportion ot lib 

 in thi-e individual-. For the purpose of comparing the 

 ratio in hybrid mice \\ith that in hybrid rat-, \on Guaita'- 

 iv< ord- ha\e been collected and the -e\ ratio- calculated tor the 

 indi\ idual- in each ^ein -r.n ion. The data thus obtained 

 -ho\\ n in tin- l"<>lln\\ in- table. 



i | 



I Al;i : I . 



. I \ I \ I 'K II V1IKII' \1 



According tO these : M'li (".uaila oblained a total 



407 h\ briil miie; but he gives the sex of only ; v v> indi\ idual-. 

 ot \\hich I s 'i were male- and K.; u ere female-. In ihi- !<> 



lubrid-, thei< n 113.17 males to 100 females. Thi- 



ratio i- iindoiibtedK higher than that \\hich i- normal 

 cither nl" the t\\o species \\ith \\liirh the e\| >erinieiit - be^an. 

 Sclnill 'lind a neaiK f|iial | u'o] oiM i-'ll <>!" tin - in 



over i ,000 albino mice that had been bred under dittermt en\ iron- 

 mental condition-: a -iniilar n-latioii betueeii the .\i-ted 

 in the l.o ualt/in- mil e bred b> \'erk-- '07 



lxa\nioiid and Maud I >. Pearl '08 have tabulated over two 



hundred tlmu-and records !' legitimate birth- i.ccurriiu in the 

 cit\ ul" Hueiio- .\\re- during the years [896 [905 inclu-i\e. in 

 order to ascertain \\ he t her tin re i- a teiideiirv toward- an 

 i\e inoductioii of ott'-prin- o|" one -e\ in CTOSS a- rompared \\ith 

 pure mating-. Their table- -how that in pure matings, either 

 anioti- Argentine, Italian or ^pani-h -lock, the number ot m 



