268 CHARLES R. STOCKARD 



sumption is not made solely from the material presented in the 

 present paper, but from the facts furnished by these experiments 

 together with the observations made upon the large number of 

 Cyclopean eyes and brains which the writer has studied during 

 the past several years. 



Various authors have at different times thought that cyclopia 

 was due to a fusion of the eyes after they had arisen from the 

 brain. The earlier in development the fusion occurred the more 

 intimately associated the two eye components became. This 

 view has been proven incorrect by actual observation on Cyclo- 

 pean monsters where it is found that the cyclopean condition 

 of the eye, whether large and hour-glass shaped or of small size 

 resembling a normal eye, is present from the earliest appearance 

 of the optic vesicle from the brain. ' In other words, the several 

 degrees of the cyclopean eye come off from the brain in their 

 final conditions. 



The idea of the fusion of the eye parts was deep rooted, how- 

 ever, and now exists in the recent views of Spemann in a refined 

 form. Spemann believes, as several others had previously sug- 

 gested, that cyclopia is due to an absence of non-ophthalmic 

 tissue in the median region of the medullary plate or groove. 

 This lack of median tissue allows the eye anlagen which he 

 holds to be lateral in position, near the borders of the medullary 

 plate, to come together and fuse iii the median plane and later 

 give rise to a cyclopean eye. Cyclopia, according to this idea, 

 occurs in a more or less passive manner, and is, after all, actually 

 a fusion of the eye anlagen of the two sides during development. 



I am certain that this fusion explanation which has now been 

 forced entirely back into the medullary plate, is as false as* its 

 bolder predecessor which assumed the fusion to take place out- 

 side of the brain tissues after the optic vesicles or cups had 

 arisen. Spemann did not advocate this late-fusion view, but 

 claimed from his beautiful experiments on Triton that the cy- 

 clopean eye arose out of the medullary tissues in its final 

 condition. He now, however, assumes the role of a most ardent 

 supporter of the fusion of the optic anlagen within the medul- 

 lary plate. 



