ORIGIN OF 'independent' LENSES 351 



It is very significant that free lenses are found only in tera- 

 tophthalmic embiyos. No case has yet been recorded of a free 

 lens in the presence of two normal, perfect eyes, while such a 

 lens may occasionally be found in the presence of both eyes if 

 the latter exhibit some structural imperfections. And in such 

 cases of monophthalmia asymmetrica, where the single lateral 

 eye is in perfect structural harmony with a normal eye, a free 

 lens, if found, is always on the side lacking the eye. Briefly it 

 may be said that free lenses do not occur where there is no eye 

 defect. This rule is so constant that some correlation between 

 the eye defect and the 'independent' lens must necessarily be 

 assumed. Granting this (and the evidence to prove just this 

 point, is, indeed, overwhelming) it might be expected that if 

 it were possible to determine the nature of the defect, i.e., the 

 mechanism which causes it, we would at the same time obtain a 

 very definite clue towards the genesis of the free lens. 



I have attempted an analysis of the nature of the defect which 

 leads to teratophthalmia, and, on the basis of very definite and 

 constantly increasing evidence, have arrived at the conclusion 

 that we are here dealing with a destructive process of dissocia- 

 tion of parts of the blastoderm. The nature of this process, which 

 I have termed blastolysis, has been very briefly outlined in two 

 of my previous publications (Werber '15 b and '16 a) while a 

 more complete treatment of the subject will be found in a paper 

 now in press (Werber '16 b) to which the reader is particularly 

 referred. 



For the sake of clearness in the following presentation it may 

 be stated, however, that blastolysis either destroys part^or all 

 of the germ's substance or it may dissociate and disperse frag- 

 ments of the latter. 



A careful study of the morphology of teratophthalmic em- 

 bryos has yielded unmistakable evidence that all of them are 

 due to a defect of blastolytic nature in the anterior region of the 

 head. In other words, the formation of terata of the eye comes 

 about through destruction of parts intermediate to the earliest 

 anlagen of the eyes or of parts of the latter. The most striking 

 evidence for this blastolytic process is dispersion of fragments 



