552 E. I. WERBER 



ndheren oder ferneren Umgebung geiveblich und formal zu differenziren 

 vermogen, und dass dies sogar in anndhernd normaler Weise geschehen 

 kann. Daraus geht hervor, dass die Differenzierimg dieser Theile an 

 sich nicht eine Function der Wechselwirkung zwischen ihnen und den 

 andern Theilen ist. 



These views of Roux apply very well to a great many tera- 

 tomata which I have recorded, and among them the 'soUtary 

 eye' and the 'isolated eye' as w^ell as to the case described by 

 Loeb, to which I have referred above. 



The 'solitary eye' and the 'isolated eye' are experimentally 

 produced teratomata analogous to some well known spontaneous 

 teratomata (e.g., 'dermoid cysts') in which hairs, skin, glands, 

 and jaw fragments with well formed teeth can be found. Accord- 

 ing to Schwalbe ('07, part II, p. 99) eye parts have been repeat- 

 edly found in teratomata. Both Roux and Schwalbe regard 

 such formations as striking evidence for the great capacity for 

 self-differentiation possessed by parts of the embryo. In the 

 light of this well supported view the morphogenesis of teratomata 

 loses all of the mystery which has so long surrounded it. It is 

 certainly not more difficult to comprehend than the differentia- 

 tion of neurones from a minute fragment of medullary plate 

 tissue explanted in Harrison's ('07, '10) pioneer experiment into 

 a favorable nutritive medium (lymph). In both cases fragments 

 of a primordium survive and differentiate fully, if nutritive and 

 other conditions necessary for the continuation of life remain 

 essentially unaltered. 



It follows from what has been said that the morphogenesis 

 of some teratomata ('dermoid cysts,' 'solitary eye,' 'isolated eye') 

 can be accounted for only by a very high ability for 'self-differen- 

 tiation' of metablastolytic fragments of the embryonic primor- 

 dium. The conclusion is also evident that at a very early stage 

 of development (coincident probably with the teratogenetic time 

 limit) the parts of the embryonic primordium are already very 

 sharply predetermined in regard to their histogenetic and organo- 

 genetic potencies. 



