434 Duplicate Twins and Double Monsters 



fined to such cases as hyperdactylism, but Tornier in a later paper, oi, 

 wishes to go much farther than that and asserts that all cases of double 

 monsters (Zwillingsbildungen) arise in the same manner, and cites, to 

 illustrate his meaning, not only individuals with two heads, and those 

 with two faces (the so-called "Janus-monsters"), but also typical thora- 

 copagi. As this theory presupposes an inequality in the value of the 

 two components, since one must be the " Stammindividuum " from 

 which the second or " Ueberzahliges Individuum " must arise second- 

 arily, it is hard to reconcile with it the exact equality in the development 

 of the two components in the overwhelming majority of cases; and as 

 separate twins of the duplicate type are so closely related to the most 

 complete double monsters, they also must be included in the theory, a 

 supposition apt to give rise to endless dispute among two people thus 

 related as to which was the " Stamm-'^ and which the " Ueberzahliges- 

 Individuum." 



VII. — A most unique theory is that of Beard, which he develops in 

 connection with his original biological doctrine of multiple germ-cells. 

 He considers that the early blastomeres of a metazoon form " an asexual 

 foundation or larva, the pliorozoon, upon which the germ-cells, and 

 with those an embryo, take their origin." ISFormally one of these cells 

 develops into an embryo, a mere incident in the life-cycle, but occasion- 

 ally two or more may thus develop. Thus " if two primary germ-cells 

 undergo normal development, the result is the production of identical 

 twins." An attempt on the part of two germ-cells thus to develop but 

 with abnormalities on the part of one produces a more or less rudi- 

 mentary embryo, which may form any grade of morbid growth from an 

 embryoma to an ordinary tumor or cancer. Wilms has conclusively 

 demonstrated that, for example, all gradations from a highly-organized 

 embryoma down to a simple sarcoma may be met with. In this discus- 

 sion Beard plainly has in mind the various forms of parasitic monsters 

 alone, since in all of his descriptions of compound forms one component 

 is normal and the other reduced. There is no doubt that, granting his 

 theory in the first place, there would be some logical explanation also 

 for diplopagi, and it will be of interest to see what this author will do 

 with this most important group of composite monsters. 



YIII. — As opposed, at least in some particulars, to all of the above 

 hypotheses is that which sees the cause, both of separate duplicate twins 

 and of diplopagi, in the total or partial separation^ of early blas- 

 tomeres, PROBABLY OF THE FIRST TWO, as advocated in the present 

 paper. This view as extended to diplopagi seems to have been first 

 clearly enunciated by Bateson, 94, who says : " It is now a matter of 



