ORIGIN OF MONSTERS. II 429 



degree of this action, for they, too, range from apparently sym- 

 metrical, well formed double embryos through various degrees 

 of deformation to highly defective and grossly malformed double 

 monsters (figs. 1 to 13). 



Among some other points which would also seem to call for 

 explanation is the often recorded unequal size of the components 

 of a duplicity where two whole slightly conjoined or entirely 

 separate embryos have developed (figs. 1, 2, 3, 4, 6, 7, 8, 9, 10, 

 ll). 18 In my opinion the only explanation possible for this 

 phenomenon is that apparently even less than one-half of the 

 entire embryonic primordium is still totipotent in teleosts just 

 as Eataillon (I.e.) has found this to be the case in Petromyzon. 

 In the case of our double embryos I would further suggest that 

 after the splitting of the germ into two parts one of them has 

 apparently sustained further blastolytic lesion which, however, 

 while dwarfing it in size, has not diminished its totipotency. 



In this connection it may be well to consider also the some- 

 times very striking differences in degree of malformation be- 

 tween the components of a duplicity (figs. 2, 4, 8, 9, 10 and 

 11). In accordance with our interpretation of the genesis of 

 malformations (Werber, '1G) it will have to be assumed that the 

 more deformed component was subject to blastolytic action in 

 a higher degree than the less deformed one. The above men- 

 tioned difference in size between components of the same du- 

 plicity is just another effect of this simple principle. I am, how- 

 ever, unable to account for these differences in degree of action 

 on duplicates of the same germ. 



Yet these differences (both in size and degree of malfor- 

 mation) between components of the same duplicity I regard 

 as important insofar as they would seem to furnish a clue to 

 the morphogenesis of the so-called 'parasitic double monsters'. 

 For, granting an - early and intimate secondary fusion of primor- 

 dia duplicated by blastolysis, and that one of these double 



18 Similar observations on very young double embryos have been made also by 

 Klaussner ('90) in the chick and in the lizard Lacerta viridis and by Dareste 

 ('91) in the chick, while one such double embryo of the chick is in my 

 possession. 



