413 Duplicate Twins and Double Monsters 



in which the two components are the duplicates of one another' and 

 S3aiimetrically united, namely that here a similar tendency to separation 

 has been left incomplete^ causing a doubling of those parts only in which 

 the interrelations have been severed. This hypothesis^ which is the 

 natural outcome of the recognition of these components as duplicates, 

 finds its best corroboration in the fact that the cases may be arranged in 

 graded series, with almost imperceptible differences between them, and 

 ranging from single individuals with a duplication of some median part, 

 to two individuals united by a slight bond, and thence to free duplicates. 

 Diplopagi do not, however, allow themselves to be arranged in a single 

 series, but in several, in which the two components bear different, although 

 always symmetrical, relations to one another, referable to the various 

 geometrical possibilities in the manner of separation and consequent 

 relative position of the first two blastomeres. 



This matter may be made clear by an inspection of Plate A, in 

 which the various known forms of diplopagi are represented in diagram- 

 matic form and arranged in graded series to show their mutual rela- 

 tionship. 



These series and the cases representing them are as follows : 



A. — Separation fkom Above Downw^aed; also in Some Cases 

 FROM Below Upward; Components Placed Laterally. 



A. I. — A normal single individual, the right and left halves of which 

 are represented by the colors black and white respectively. In the em- 



" Although in the great majority of diplopagi the components are evidently 

 physical duplicates, I have collected the three following cases in which differ- 

 ences seem to have been noted. (1) Fare's case, 1570, baptized Louis and 

 Louise, (2) The Irish sisters, 1827 (v. p. 40J ), of whom one was said to be dark 

 haired, the other fair, and (3) Marie-Rosa Drouin, 1878, one of whom was 

 said by MacCallum to resemble the father and one the mother. Should those 

 cases be substantiated they would necessitate a modification of my theory, 

 at least in those special cases, but the reports are hardly conclusive enough to 

 be of serious import. Fare's case was reported over three hundred years 

 ago, and at a time when feminine names in France were assumed by men. 

 There is no statement to the effect that they were of opposite sex. The other 

 cases are based upon general impressions, in both cases derived from new- 

 born infants, and hence are somewhat unreliable. The most conclusive test 

 to prove or disprove the similarity of the components, both in diplopagi and, 

 when possible, in parasitic monsters, is that of the palm and sole configura- 

 tion, and it is to be urged that, whenever opportunity affords, careful prints 

 be taken of the palms, soles and fingers of compound monsters. Such data 

 will prove of the highest importance in the present line of argument. 



