Principles of Heredity 175 



Polecat are two distinct species, because, " as everybody 

 ought to know," 



" The result of a cross between albino and normal [of 

 one species] is always a constant one, namely an offspring 

 like the father at least in colour* " 



whereas in crosses (between species) this is not the case. 



And again, after reciting that the Ferret-Polecat crosses 

 gave intermediates, he states : 



" But all this is not the case in crosses between albinos and 

 normal animals within the species, in which always and without 

 any exception the young resemble the father in colour t." 



These are admirable illustrations of what is meant by 

 a "universal 3 proposition. But von Fischer doesn't stop 

 here. He proceeds to give a collection of evidence in proof 

 of this truth which he says " ought to be known to every- 

 one." He has observed the fact in regard to albino mole, 

 albino shrew (Sorex araneus), melanic squirrel (Sciurus 

 vulgaris), albino ground-squirrel (Hypudaeus terrestris), 

 albino hamster, albino rats, albino mice, piebald (grey- 

 and-white or black-and-white) mice and rats, partially 

 albino sparrow, and we are even presented with two cases 

 in Man. No single exception was known to von Fischer {. 



* "Das Resultat einer Kreuzung zwischen Albino- uud Normal- 

 form ist stets, also, constant, ein dem Vater miudestens in der 

 Farbung gleiches Junge." This law is predicated for the case in 

 which both parents belong to the same species. 



t "Dieses Alles ist aber nie der Fall bei Kreuzungen unter 

 Leucismen und normalen Thieren innerhalb der Species, bei denen 

 stets und oline jede Ausnahme die Jungen in Farbung dem Vater 

 gleichen." 



J He even withdraws two cases of his own previously published, 

 in which grey and albino mice were alleged to have given mixtures, 

 saying that this result must have been due to the broods having 

 been accidentally mixed by the servants in his absence. 



