i\(\ LiTTLK 2H« 



VII. Criticisms ok kxistino iiYiM»TiiF><>>i to kxim.ain tiik 



iK^crUHKNCE OK TOKTolSK-SIIKM. MAI.KS. 



(1 ) l\)!ic4uttor'.s hy|x»thfHi.s, jus jiln-july |M>intr(| nut, nM|uinM "cniswiii^ 

 ovor" ill tluMualr lK*twi*i'n A' jiikI ^ chnnnn.mnncs jic<»M«litinn imi .shuwii 

 to oxiat in giiinot<)j;i»m\siH of any A'^ nmlr rnriii. It. fMitlnr fails to 

 acctMint for {a) tlu^ comparativr infrtMjucncy tti' tintoi.sc-slnll nuilis an 

 COlM[>jinHl with alh'rrant Mack fnnalrs, {b) tlu' strrjljty of tin- majority 

 of torUnse-shi'll inah's, ami (r) their peculiar hchavi(Mir iti hnMciin^r 



(2) Ibsen's hy|K)thesis dot's away with the nee<l of crossing over in 

 the nuUo, hut fails, as does Doncjvster's hypotliesis, to meet or explain 

 point* (a), (/>), or (c) statA'd above. 



(3) Whitinj^'s hypothesis of nioditiers would not be aljle to ^'ive a 

 tortoise-shell male which acconlin^^ to his formula wouM be A' }'^ with- 

 out iwldinj; a fiwtor for black t^) the formula ^nven by him to be carried 

 in the A' ^imete. It further would supjH»se that by selection (which 

 iindoubttMJly ha,s t>ccurred) it would be possible t(» transmit the necess;iry 

 motiitiers t<.) a considerable number of his male progeny, thus fornnng 

 torU)ise-shell males — and this, though great efforts have been made, hjus 

 provLHl imjx)ssible. Whiting's hypothesis, like those of Doncaster and 

 of Ibsen, takes no account of the sterility of the majority of tortois<'-shell 

 males. 



(4) Wright's hypothesis is that t(jrtoise-shell males are really A' A' 

 individuals in which the abnormality lies not in the cohmr but in the 

 sex. He likens them to certain sex intergrades alre;uly described in 

 some forms by other investigators. This hypothesis meets trouble when 

 a fertile tortoise-shell male is encountered. It also is contrary to th<' 

 evidence obtained by Bridges who shows that in Drosophila A' A' fonus 

 are females, even though they contain other abnormalities of chromosome 

 distribution. 



VIII. Summary and conclusions. 



(1 ) The genetic constitution of the normal colour varieties of cats ;is 

 regards yellow and black pigmentation appears to be as follows: Ji = a 

 factor producing black pigmentation, }' = a factor which restricts black 

 from the coat, y = a fiictor allelomorphic to Y^ and hy[)ostatic to it, 

 allowing black pigment to extend to the coat. 



17/A' J7;A' Yellow female 



17^V e Yellow male 



yliX ylLX lilack fern ah- 



yHX Black male 



YliX yftX Tortoise-slj.ll fem.iU- 



Joum. of Gen. vui 20 



