432 E. I. WERBER 



Granting, however, the possibility that up to the time of 

 gastrulation the mammalian (and Sauropsid) ovum is 'capable 

 of being divided into two or possibly more equi- and totipotent 

 parts, it would remain to be shown that the parts thus separated 

 may, as in Petromyzon and teleosts, be able to form any kind 

 of duplicity, depending upon the degree of separation, the dis- 

 tance between the parts separated and the angle of their re- 

 spective convergence. , There is reason to believe that no dif- 

 ferences should exist in this regard between the teleost ovum 

 on the one hand and the Sauropsid and mammalian ovum on 

 the other hand. For, as Fischel sets forth (I.e., p. 274), the 

 processes leading to the formation of the embryonic body (sepa- 

 rate anlagen for the head and trunk, the latter formed by con- 

 crescence of two lateral parts) being in principle very much the 

 same in all vertebrates the morphogenesis of double monsters 

 in teleosts may — at least with certain restrictions of secondary 

 significance — be extended to amniotes and even to man. 



These conclusions are, obviously, tentative and — in default of 

 experimental tests in mammals — they will probably remain so 

 for an indefinitely long time. Their advantage, however, be- 

 sides offering a plausible explanation, is that they may help 

 to keep alive further inquiries into the, so far inapproachable, 

 problem of diplogenesis ('twinning') in amniotes. 



It is for this reason mainly of methodological advantage that, 

 — in default of evidence to the contrary— I am inclined to hold 

 to the views above expressed in preference to Wilder's specula- 

 tions- 3 on the subject. For, while I can find no fault with this 

 writer's reasoning, I consider that his separation of the double 

 monsters (sensu stricto) from well formed, symmetrical du- 

 plicities ('orderly beings — cosmobia') and the assumed mysterious 

 origin of the latter by a sort of mutation due to ' germinal varia- 

 tion' are both unnecessary and arbitrary. The lack of defor- 

 mities in 'Cosmobia' as well as in viable monozygotic twins 

 would rather seem to indicate that while they may be develop- 

 mental products of primordia duplicated by blastotomy, they 



23 A view similar to that of Wilder's seems to have been advanced also by Bolk 

 ('06), whose paper is, unfortunately, inaccessible to me. 



