134 THE BIOLOGY OF TWINS 



striking faithfulness of position and detail in two or 

 more individuals of a set and were totally absent in 

 others of the same set. Sometimes all four individuals 

 showed these characters, but to a very different extent 

 or in different positions. For example, the doubling 

 might be unilateral in one pair of twins and bilateral 

 in the other, or the character might involve a dozen 

 scutes in some and only one or two in others. The real 

 significance of this situation did not become apparent 

 until it was found that these somewhat anomalous 

 arrangements of scutes, which in general we call ''dou- 

 blings," were definitely inherited. It appears that there 

 is a close genetic relation between "scute doublings," 

 where the anomaly affects only one armor unit (an 

 incipient doubling), and "band doubling," where from 

 two to many units are involved. Sometimes band 

 doubling in the mother is inherited in the offspring as 

 scute doubling, and vice versa. Quite often the expres- 

 sion of the character may differ within the set of off- 

 spring, so that a band doubling or a scute doubling in 

 the mother may be inherited in some offspring as a 

 band doubling and in others as a scute doubling. 



In general it may be stated that in all cases except 

 two, which are quite doubtful, when a mother has 

 either a scute or a band doubling, one or more offspring 

 in a set show a doubling. There are three categories 

 in one homogeneous collection of 140 sets of quad- 

 ruplets, in which the condition of the mother is definitely 

 known : 



(a) Those in which both mother and offspring show 

 doubHng; of these there are 56 sets, 29 female and 

 27 male. 



