CYCLOPIA IN THE HUMAN EMBRYO. 13 



new relations of these primordia with the resulting abnormal forms. Thus, as 

 one examines these developing embryos, from the time the eye primordia are 

 first visible in the living specimens under the binocular microscope, they appear 

 to have the same amount of fusion or loss of eye that is clearly to be found in the 

 same individual at later stages and at the time of hatching. So we can explain 

 these cyclopean forms by a fusion of the primordia of the two eyes immediately 

 after the operation, even though at this time no primordia are visible. Differentia- 

 tion of the eye-tissues evidently occurs some time before it is visible by our crude 

 microscopic methods. 



Briefly summarizing the experiments of Stockard and Lewis, it may be said 

 that Stockard produced cyclopia by immersing Fundulus eggs in a magnesium 

 solution before the formation of the germ-ring, while Lewis operated upon the 

 embryonic shield after it had arisen from the germ-ring. According to Stockard, 

 the magnesium solution possesses a decidedly anesthetic effect and inhibits the 

 growth of the optic out-pocketings ; and therefore the condition of cyclopia must 

 be present before the formation of the optic cup which he believes to be median 

 the anesthetic effect preventing the medial cup from dividing, thus bringing 

 about the cyclopean condition. According to Lewis, the optic primordia are 

 brought together through the removal of a small amount of tissue which normally 

 lies between them. The primordia then unite and produce all degrees of the 

 cyclopean condition. For practical purposes either theory will suffice to explain 

 the condition as found in man, and there is at present no evidence which can 

 decide which of the two is correct, for I may add that (as Dr. Lewis informs me) 

 the optic primordia arise very close to the ventral midline of the brain, being 

 separated by only a few cells. 



Stockard has recently attempted to define more accurately the eye primordia 

 in Amblystoma by operating upon the medullary plate. First of all, he found that 

 pricking the medullary plate, as Lewis pricked the germ-shield in Fundulus, had 

 no effect whatever upon the growth of the eyes. They invariably grew in a normal 

 way. He then removed various parts of the medullary plate and found that the 

 removal of a median strip about one-fourth to one-third the width of the medullary 

 plate resulted in eyeless embryos. The entire eye primordium apparently lies 

 within this median strip. When a narrower strip was removed the embryos de- 

 veloped with one eye, with defective eyes, or with no eyes at all. From these 

 experiments he concludes that the primordia of Amblystoma arise in the antero- 

 median portion of the medullary plate, and not from two independent primordia, 

 as is believed by Lewis. 



It may be added that the earlier papers of Lewis and of Stockard were written 

 partly to demonstrate that cyclopia is not an hereditary but an acquired quality. 

 This opinion is much at variance with that of Wilder, who upholds the hereditary 

 theory. In this relation may be stated that there are two records of cyclopia in 

 twins. One, by Ellis, is referred to by Ashfeld on page 283 and is also illustrated 

 in figures 11 and 12, plate 47, of his Atlas. The other is by Van Duyse, and is 

 referred to by Schwalbe and Josephy on page 210. The Van Duyse case is inter- 



