516 THE AMERICAX NATURALIST [Vol. LV 



huHvidiials used for hybridization were observed as to 

 their tumor incidence and g-enerally found to beliave in 



Soiiicriiiies \vc ]i> lii'idizcd sisters with tlic same male, 

 (»r we iisrd coiisrcutivcly the same mah' with females 

 fi-om strains wiiicli dilfered much in theii' tumor rate. 

 The i(-iihs ill tile hybrids could usuallN' be foreseen from 

 the known tuiiioi- rale ;ind tumor a.uc of the parent up 

 to a eertniii point of variability. Tlie eases in which the 

 -tr;iin> used for h\ hridiza! ion had a simihir tumor rate 

 couhl he con^idci-ed a> emilrol>. Ilei'e a similar tumor 

 iiieideiiee ou.uht to lia\e ajjpeared in the offspring and 

 tliis i> what usually oeeurred. 



As we stated ahove. tile reMilt. of hybridizations aiv 

 typically intermediate, but the i-ate> and tumor a-e> of 

 the cro»es may in some cases appi-oach the parent with 

 the hi-hei- rale, in other eases the parent with the h)wer 



We shall cite two exami)les, where the offsijring- re- 

 sembled the parent with the higlier tumor rate. (1) A 

 >on of a tumor mou>e Xo. lUO, belonging- to thfe strain 

 s — (lermaii, wa> mated to a White Cream female. 8 + 

 (ierman was a >train fairl\ rich in tumors and the par- 

 ti.-ular tninilv u^ed liad a tunioi" rate of 4:5 ])er cent. The 

 tumors api.eared early in life. In the White Civani us.mI 

 in tlii> ease tumors were extremely I'are and they ap- 

 ,M.ared late in life. Among the offspring 1> female mice 

 lived lon-en..u-h to he inchnh'd in the record^. Of these 

 1) miee, .') die<l with tumors, 1 in the first and 4 in the 

 second aue ])erh)d. In thi> ea>e the inrtuenee of the father 

 i> undoul)tedlv verv marked. In the Cream >traiu such 

 a tumor rate wa> nev.-r obs.-rved even among isolated 

 familie>. The tumor a-e ed" tlM> hybrid i>. Icwever, in thi^ 

 ea>e probably aHVeted by the mother. 



(L'i In thr' second ens.' whieh We wish to mention, an 



Knuiish Sable, who have normally a very hiuh tumor 

 rate, was mat<'d to females belonging to the su1)strain 



