396 Duplicate Twins and Double Monsters 



could, but I doubted it; they used to fool her often. When they were 

 babies she kept different colored beads around their necks to tell them by. 

 They always weighed on the same notch until they were seven years old, 

 then one gained half a pound more than the others." ^ 



Duplicates among Lower Animals. — It is altogether likely that 

 the phenomena of duplicate twins and other similar combinations are not 

 confined to man but that they are more or less common among the lower 

 animals. In mammals that produce several young at a time, it is prob- 

 a.ble that the components are mainly fraternal, but it is also likely that 

 there may be occasionally one or even more sets of duplicate components 

 in a given litter among their normal and contemporaneous brothers and 

 sisters. 



Observations upon this point are best made by a study of the intra- 

 uterine relationships, although in piebald domestic animals there is often 

 sufficient individual differentiation to render possible observations along 

 the line of personal resemblance, characters in color and marking taking 

 the place of those in facial expression. Eegarding lower vertebrates, 

 especially birds, a large number of instances have been recorded, some of 

 which are of interest in this connection. Thus, v. Kolliker describes a 

 hen's egg containing two embryos, each with its own amnion and allan- 

 tois, but sharing betwen them a single yolk to which each was attached 

 by its own independent yolk-stalk, and M. Braun has noted a similar 

 condition in the lizard. These cases are cited by Schultze and placed by 

 him under his Case III, given above. The mature results of these would 

 certainly have been duplicate twins, either separate or united in the 

 umbilical region. For invertebrates the very numerous experiments of 

 Wilson, Morgan and many others, performed upon the alecithal eggs of 

 numerous marine forms, and in which separate individuals are formed 

 by shaking apart the early blastoderms, suggest that the same result may 

 occasionally take place spontaneously. The individuals thus artificially 

 produced are undoubtedly genuine duplicates, and the process seems in 

 every way comparable with the phenomena postulated above as occurring 

 in the vertebrates, making allowance for the complications introduced 

 in the latter case by the presence of yolk-sac and other extra-embryonal 

 organs. 



^ When they were little girls one of them confided one day to a friend that 

 she had been bathed three times that morning, while the others confessed that 

 they had not been bathed at all, an incident that emphasizes their complete 

 bodily identity at that period. 



