BOWMAN LECTURE. LXI1I 



through daughters who do not themselves show it, is 

 sometimes lacking. 



The effect of consanguinity and the facts as to sex- 

 limitation can both be considered in relation to the 

 Mendelian theory. According to this theory of inheri- 

 tance, a character and its opposite or absence is repre- 

 sented in the gametes by particles ; this at least applies to 

 certain characters, pathological as well as physiological. 

 These particles occur in even numbers or pairs in each 

 gamete. The members of each pair may be similar (both 

 representing presence of the character, or both representing 

 its absence), or may be dissimilar (each pair containing one 

 of each kind). In the fertilised germ the pairs derived 

 from the gametes, so to speak, change partners. The 

 constitution of the particles in the resulting zygote 

 depends upon that in the original gametes ; the zygote 

 may contain only pairs representing the character, only 

 those for its complement or absence, or a hybrid between 

 the two. For convenience, one of the characters (or its 

 participate representative) is called " dominant " (D.D., 

 Fig. 6 A and B) , because when it unites with the other, or 

 " recessive " (R.R., Fig. 6 B), the resulting hybrid shows 

 only the former character, although carrying both (D. R., 

 Fig. 6 B). The other character, the " recessive/' although 

 potentially present, is undeveloped and does not show. 

 In some cases, however, the " recessive " factor does 

 show, and then the visible result is an intermediate form. 

 As I understand the matter, the vital point in Mendel's 

 interpretation of the facts of heredity is the separate, and 

 numerically equal, p articulate representation of qualities 

 in the gametes. Visible dominance is not an essential 

 part of the theory, because intermediates occur showing 

 both the constituent qualities. The terms " dominant " 

 and "recessive" are convenient and useful, but must be 

 dissociated from any conception of what may be either 

 " good " or " bad/' " desirable " or " undesirable," 

 "strong" or "weak " ; indeed, as we shall see presently, 

 in some cases the disease or defect behaves as what Mendel 



