CYCLOPIA IN THE HUMAN EMBRYO. 



united at once, but in a few instances a double eye was formed. Later Spemann, 

 making similar experiments, also produced cyclopean embryos. In some of 

 Spemann's experiments triton eggs were ligated in the sagittal plane during seg- 

 mentation, and frequently embryos with double heads resulted, one or both being 

 cyclopean. Spemann believes this experiment proves that in its differentiation 

 the cyclopean eye is defective from its beginning and is not produced by con- 

 crescence of two eyes which started to develop normally. Levy also produced 

 cyclopean monsters by cutting off the front of the head of triton Iarva3. In the 

 course of two weeks the two eyes approached each other and formed a double eye, 

 but they did not fuse. However, the pigment layer was destroyed, or absent, 

 at the point of contact. The two optic cups touched each other, but did not unite. 



In 1906 Harrison produced a new variety of cyclopia by removing the entire 

 brain from frog embryos. In these specimens the eye moved to the back of the 

 head and appeared to unite in a single vesicle in the region usually occupied by 

 the pineal eye. These specimens are still unpublished. 



By pricking the extreme anterior end of the embryonic shield in Fundulus 

 eggs, Lewis found that many of the eggs developed into cyclopean monsters. All 

 grades of defective eye were formed from a double eye and hourglass-shaped 

 eye with two lenses to oblong eyes with two lenses or with but a single lens. The 

 optic cups blended absolutely, thus apparently showing the mode of develop- 

 ment of these eyes. Lewis also found that in many of the embryos the brain had 

 not been injured at all, but that the prick had destroyed the nose only. This 

 experiment seems to show conclusively that it is the absence of tissues between 

 the eye primordia which allows them to come together and unite, and that a 

 rudimentary brain is unnecessary. 



In his remarkable experiments on the artificial production of a single median 

 eye in the fish embryo by means of sea-water solutions of magnesium chloride, 

 Stockard found that 50 per cent of the embryos developed cyclopia. In these 

 embryos the optic cups were fused at an early developmental stage, much as was 

 the case in Lewis's specimens, in which the embryonic shield had first been pricked. 

 The union of the two cups formed a large compound eye, which in turn derived 

 its lens from the epidermis immediately overlying it in the midline of the embryo. 

 How the magnesium acts upon the embryo is not clear from Stockard's descrip- 

 tion. No doubt it will be found that it retards the growth of the frontal process, 

 much as in Lewis's experiments. The salt, however, acted upon the whole body 

 of the embryos, for their development was retarded, thus making them smaller 

 than usual, and their circulation was feeble, but they did not die. In these em- 

 bryos, as in Lewis's specimens, the growth of the brain was normal. The remark- 

 able experiments of Stockard set at rest all germinal theories of cyclopia and prove 

 that every egg has in it the power to develop cyclopean monsters. 



These experiments, as well as the numerous pathological embryos with 

 deformed heads and faces which I have studied, prove at any rate that in the 

 formation of many monsters there is an extensive destruction and shifting of 

 tissues. This is also well illustrated in the production of club-foot in the human 



