POSITION OF OPTIC ANLAGE IN AMBLYSTOMA 255 



The only evidence to draw upon is the interesting experiments 

 of Lewis, in which it was found that cyclopia sometimes resulted 

 in Fundulus embryos when the anterior end of the embryonic 

 shield was injured by pricking. Lewis also interpreted these 

 defects as due to a fusion of the optic anlagen, and had sug- 

 gested, as Spemann now does, that the chemicals used in my 

 experiments suppressed the development of niedian tissue in the 

 medullary plate and thus caused the eye anlagen to come to- 

 gether, fuse and produce cyclopia. There are a great many 

 strong objections to this hypothesis of Lewis and Spemann which 

 have been enumerated in my previous papers and to which I 

 shall take occasion to refer briefly in the following discussion. 



An objection of primary importance to the idea of cyclopia 

 as a result of the coming together of lateral anlagen through a 

 failure of intermediate tissue to form is the fact that cyclopean 

 eyes are rarely in size and extent equal to the sum of the two 

 normal eyes combined. A cyclopean eye is, as a rule, little if 

 any larger than one normal lateral eye and in fact is often much 

 reduced or actually minute in size as compared with a normal 

 eye. This fact indicates most decidedly that eye material, as 

 such, has been, injured or arrested in its development and differ- 

 entiation. One is then scarcely warranted in assuming that the 

 defect is solely due to a failure in formation of material between 

 the eyes, 



Spemann has found, although he locates the anlagen in the 

 wrong place, that not only is the eye anlage definitely localized 

 in the open medullary plate but actually the tapetum nigrum 

 is distinct from the other retinal layers. How then could absence 

 of material between the lateral eye anlagen cause less eye mate- 

 rial to arise? 



The differentiation of these prelocalized anlagen require defi- 

 nite amounts of energy. Any treatment that weakens the devel- 

 oping embryo at certain periods in a definite way renders the 

 eye anlagen incapable of differentiation so that they do not arise 

 from the brain. 



The entire problem is readily open to experimental test. The 

 contention may resolve itself into the question: Where are the 



