ORIGIN OF MONSTERS 527 



mental evidence, but even lacking this important basis, it would 

 seem far more reasonable and safer and far less arbitrary than 

 the unwarranted claim that the 'optic anlage' is median and 

 that the optic stalks are a part of it. Granting, however, that 

 my view is correct — and there is at least a very high degree of 

 probability in it — it is easy to understand that optic stalk tissue 

 may be partly median in origin while the optic vesicles come 

 from antero-lateral regions of the medullary plate. In this case, 

 then, it is also evident that the position of the optic stalks and 

 later of the optic nerves and chiasma ventral to and outside of 

 the brain can not, by any means, be regarded as evidence of the 

 median origin of the eye anlagen. Stockard's own diagrams 

 (figs. 6 and 7, p. 275)'' which are to prove that the eye anlage is 

 primarily median in position would rather seem to support my 

 arguments for the lateral origin of the latter, while his diagram 

 in figure 8 (p. 276) most decidedly portrays a condition which 

 is impossible, not, because the optic stalk tissue is (partly) of 

 median origin, but because it is not a part of the eye vesicle. 



From what has been said so far, it is obvious that Stockard's 

 assumption of the single condition of the optic anlage and its 

 median position in the medullary plate as a basis for the morpho- 

 genesis of synophthalmia and cyclopia is untenable. 



From a study of my own abundant material in sections as 

 well as from a careful scrutiny of the views presented by pre- 

 vious writers on the subject I have convinced myself that a 

 rational analysis of the morphogenesis of synophthalmia and synoph- 

 thalmic cyclopia must be based on Spemann's ('04, '12) and Lewis' 

 ('09) theory of a fusion of early (pre-vesicular) eye anlagen, due to 

 a defect of intermediate tissue. This conclusion I have reached 

 in spite of the indisputable fact that the fusion theory is in- 

 adequate in the case of perfect cyclopia and that the nature of 

 the defect that precedes the fusion has not yet been made quite 

 clear. 



In the following I shall attempt an analysis of the morpho- 

 genesis of teratophthalmia which* is based on a recent physio- 



^ Owing to the great importance of the subject here discussed the reader is 

 advised to consult Stockard's ('13) diagrams, without which this discussion 

 may perhaps not be quite intelligible. 



