1 66 THE BIOLOGY OF TWINS 



and just the kind of thing one might look for in con- 

 joined twins. Quite unexpected, however, is the occur- 

 rence of the odd pattern in the right sole of Mary. 



I am inclined to interpret the cause of this aberrant 

 sole pattern in the light of similar conditions found in 

 armadillo quadruplets. There it was not unusual to 

 find that one or more fetuses in a set inherited a pecu- 

 liarity while others did not. This was explained as an 

 instance of somatic segregation taking place during the 

 early cleavage divisions. Evidently this is an instance 

 of a similar phenomenon occurring in conjoined twins. 

 In principle this is not different from the unilateral 

 reappearance in an ordinary offspring of a peculiarity 

 inherited from a parent. The case is one of very 

 special interest, since it is the only one of twins on 

 record where the embryonic membranes were studied in 

 correlation with the somatic resemblances. It was 

 ascertained that "there was a single chorion without 

 trace of a separating partition, and the placenta was 

 bilobed, and nearly as large as two normal placentae." 

 The umbilical cord was single for ii cm. from the pla- 

 centa, forking into two branches, one a little larger 

 than the other, running to the two individuals. It is 

 only to be regretted that the palm and sole patterns 

 of the two parents were not recorded. Possibly these 

 data, quite crucial in character, I believe, may be yet 

 available; it would probably demonstrate the fact of 

 somatic segregation of parental characters. 



Variations on brain convolutions and in hair arrange- 

 ment in duplicate twins. — A significant paper by Sano^ 



^ F. Sano, Philosophical Transactions of the Royal Society of London, 

 CCVIII (1916). 



