VARIATION AND HEREDITY IN TWINS 133 



are inherited in mosaic fashion. There is every evidence 

 of an unequal distribution of inherited units among the 

 cleavage products of the single germ-cell. This results 

 in an interindividual segregation of inherited characters, 

 which is much like the unilateral appearance of a color 

 character in certain piebald types, where one half of 

 the face is colored, the other half white, or where one 

 foreleg is colored and the other not. This somatic 

 segregation of inherited characters is very general and 

 will be discussed more at length in a subsequent 

 connection. 



Inheritance of double bands. — The arrangement of the 

 scutes of the banded region is in general remarkably 

 regular (see frontispiece). Each band is typically com- 

 posed of a single row of scutes. A small percentage of 

 individuals show an irregularity in scute arrangement 

 consisting of parts of bands that are double, while the 

 rest are single. In Fig. 42 a number of t>^es of band 

 doubling found in a single set of quadruplets are shown. 

 Sometimes the double part is quite extensive, involving 

 a large part of the band; sometimes it consists of a 

 doubling of only one scute (third band from top to 

 right, Fig. 42). All intermediate conditions are found. 

 Band doublings may be confined to one half -band, or 

 they may be repeated on both halves; i.e., they may 

 be bilateral or unilateral in their expression. The 

 presence of irregularities of this sort furnishes us with 

 the only data by means of which we can get a really 

 definite idea of the distribution of inherited characters 

 among polyembryonic offspring. It was noted quite 

 early in comparing the individuals of polyembrsonic 

 sets that sometimes band doublings were repeated with 



