EFFECTS OF AMPHIMIXIS ON ONTOGENY 287 



There are. however, exceptions to this rule. As already 

 stated, the homologous parts of the two antimeres may differ 

 from one another; and such a difference is even frequent in 

 certain animals, though it only affects characters which are of 

 minor biological importance. Little attention has hitherto been 

 paid to the fact that many of our domestic animals have lost the 

 original synmetiy of the marking of their coats. Piebald cats, 

 dogs, horses, cows, and guinea-pigs are not uncommon, and 

 show that the symmetry of the markings may become com- 

 pletely lost by domestication. This must be owing to the fact 

 that these originally symmetrical patches of colour are, in conse- 

 quence of domestication, no longer of biological importance. If 

 the determinants for these characters varied in different ways on 

 the right and left sides, and the animal in question thus became 

 spotted, no disadvantage would thereby result, and the animal 

 would nevertheless be able to exist and produce offspring. If 

 two individuals with different piebald markings then paired, the 

 asymmetry in the coloration and markings would be increased ; 

 and as a matter of fact in many of our races of cattle no parts 

 of any two animals are alike in this respect, and the same is 

 true with regard to many dogs and guinea-pigs. We know how 

 important these markings and coloured patterns may be for the 

 preservation of individuals and species in the natural condition, 

 and are therefore justified in attributing the retention of the 

 symmetry to natural selection, and its loss to panmixia. 



Certain facts with regard to the metameres, or successive parts 

 of which the body of a segmented animal is composed, show 

 that tiie maternal or paternal characters may preponderate in 

 different segments. This naturally cannot be proved in the 

 case of Man. as the metameric .segmentation only affects the 

 bones, muscles, and nerve.s, which are not externally visible. 

 But I think I have observed that consecutive parts, even when 

 they are homologous, may occasionally exhibit different heredi- 

 tary types. A child may closely resemble its mother as regards 

 the arms and hands, and nevertheless may take after its father 

 in respect of the legs and feet. I have endeavoured to ascer- 

 tain whether any definite rules are followed with regard to 

 certain organs which are closely related to one another in 

 ontogeny, according to which the.se organs would exhibit 

 a similar combination of parental characters ; but the only 

 rule I could discover is that which relates to the symmetry 



