224 HARRIS HAWTHORNE WILDER. 



as well as mother, and sometimes a second preceding generation, 

 together with collateral lines, as represented by brothers and 

 sisters, aunts and uncles. In the work on the armadillo the 

 mothers only are known, and thus all peculiarities of the offspring 

 not accounted for by the maternal carapace, are, rightly or 

 wrongly, attributed to the unknown father. As a third advan- 

 tage, (3) largely one of convenience, may be mentioned the ease 

 with which even a very large collection of flat prints may be 

 filed and handled. This is especially noticed when a series of 

 prints are to be compared at one time. 



On the other hand, there are numerous marked advantages 

 accruing from the study of the armadillo, so many, in fact, that 

 the work is indispensible in the study of human friction ridges. 

 The way in which the results obtained in this field have supple- 

 mented the work on human twins, rendering vaguely expressed 

 ideas definite, and raising hypotheses to the category of what 

 by analogy may be considered facts, has been the subject of the 

 preceding pages. 



In their paper on the limits of hereditary control in the arma- 

 dillo (1911) the two authors often quoted offer two objections to 

 my conclusions of a similar nature, as shown in the friction ridge 

 configuration of human twins. The first, and most valid one, is 

 that "the origin of the two individuals from a single fertilized 

 egg is assumed from the facts of resemblance," while the second 

 is that "the comparison between the twins is made only after 

 years of post-natal life." Owing to the abundantly proven 

 unchangeable nature of human friction ridge configuration the 

 second objection is invalid, so that there is left but the first 

 one which may become expanded into two questions, that the 

 early conditions in the embryonic history of human twins is 

 unknown, and that in individual cases it is not usually possible 

 to find out whether they were monochorial or bichorial. 



As explained above, analogy with the very similar early stages 

 in the armadillo shows pretty conclusively that human mono- 

 chorial twins are due to a genuine polyembryony, while in some 

 cases it is possible to obtain the chorionic relations, as in the 

 case of the double monster above treated. After collecting the 

 details of a twin case from any responsible physician the case 



