POSITION OF OPTIC ANLAGE IN AMBLYSTOMA 281 



too late. The reason for the nonoccurrence of cyclopia when 

 eggs were treated at periods later than fifteen hours after fer- 

 tilization or fifteen hours before the appearance of the optic ves- 

 icles is that the optic anlagen and all other embryonic parts are 

 constantly changing during development and have passed beyond 

 the critical stage. It is not only a question of how quickly one 

 may stimulate but in what condition the anlagen are at the time 

 of stimulation. It is safe to say that cyclopia can not be produced 

 after the optic anlagen have proceeded to some definite stage in 

 their normal development. Even if Mg should penetrate all the 

 membranes within a few seconds its action could never induce 

 cyclopia in an embryo with the two optic vesicles visibly formed. 

 There was no question of the time necessary for penetration, but 

 an important question of the embryonic condition to be acted 

 upon, the critical condition of the optic anlagen. 



In the above connection it may be mentioned that such sub- 

 stances as alcohol and ether, when administered to an early embryo 

 may cause it to develop into a decided monster. A late embryo 

 or foetus may respond to the same treatment by producing an 

 individual exhibiting no gross morphological defects yet showing 

 decidedly abnormal nervous reactions, while a similar treatment 

 might exert little or no effect upon a fully formed individual. A 

 stimulus could not cause the mature individual to change into a 

 structural monster. The developmental period of administration 

 is of as high importance in determining the result as is the nature 

 of the stimulus used, unless of course the stimulus be entirely 

 destructive. 



Again Spemann misinterprets a statement regarding the action 

 of Mg. It was remarked that the cyclopean embryos develop- 

 ing in the Mg solutions were, except for the eye defects, more 

 perfect than those arising from treatments with alcohol, ether, 

 and so forth. The Mg cyclops often had apparently normal 

 brains, could swim in normal fashion, took food and reacted to 

 stimuli much as normal embryos did, while those embryos treated 

 with alcohol and ether had various defects of the brain and cord. 

 In this connection it was cited as of interest that Mayer had re- 



