Experiments with other Mammals 117 



number of black lambs is too small on the assumption that 

 chance meeting of equipotent "pure" germ-cells brings about 

 the results. 



Poulton * has given some records of polydactyl cats that appear 

 to be explicable, so far as they go, along Mendelian lines. Three 

 young were produced from a polydactyl female by an unknown 

 father. They were all polydactyl. If polydactylism dominates 

 over the normal condition, this result is simple dominance. One 

 of these individuals (F^) produced three litters (by unknown 

 fathers), in which four normal and six abnormal kittens ap- 

 peared. If the father was normal, five normal and five poly- 

 dactyl young would be expected. Thus : 



P + N 



N + N 

 2 NP + 2 NN 



Only two kinds of discontinuous inheritance that may possibly 

 follow Mendel's law have been shown for man. Albinism, ac- 

 cording to certain data collated by Castle, may perhaps follow 

 this rule. The cases referred to were albino negroes. Albinism is, 

 of course, different in this respect from white. In the latter case, 

 blending of the black and white occurs to produce mulattoes. 



The other case is that of polydactylism. Fachenheim has 

 given some statistics, 2 that Davenporf has examined from the 

 point of view of Mendelism. The accompanying table gives the 

 inheritance through three generations : 



Gen. NxP 



Mi I ~T ~T ~T I 



I. P N N(xN) P(xN) N(xN) P(xN) N(xN) PxN 



i r i ' r i i 



II. 6N 3 P4N 3 P ;N 3 N 2 P 8N 2 P aN P (xN) 



2 N 3 P 



N(xN) P(xN) N(xN) N(xN) 



i 2 N 3 N 2 P 3 N N 



1 Nature, 1883. 2 Jena Zeitschrift, XXII, 1888. 



