ORIGIN OF MONSTERS 491 



tiguous medially, but not fused. On microscopic examination 

 it was found, however, that there is a fusion of the median parts 

 of the eyes which becomes the more distinct the more posterior 

 the section examined. 



In the embryo presented in figure 4 one median composite eye 

 is to be seen, the components facing each other and enclosing 

 one lens. 



Cases of cyclopia, i.e. embryos in which the single median 

 eyes on examination in toto do not present any evidence of being 

 composite in character are presented in figures 5 to 9 and 12. 

 A comparison of these figures shows that the cyclopean eye 

 may vary considerably in size as well as in other respects. It 

 may be very large, much larger than a normal eye (fig. 5) or of 

 about the size of the latter or even smaller, and sometimes, 

 indeed, very minute (fig. 8). Furthermore, the cyclopean eye 

 may have the appearance of a normal eye, or it may vary in that 

 respect. Thus, for instance in figure 9 is seen an embryo with a 

 cyclopean eye lacking a lens, but instead showing a very dis- 

 tinct ventral duplicature of the pigment layer, which was verified 

 on microscopic examination. The ectoderm above the cyclopean 

 optic vesicle was probably defective and the optic vesicle has 

 evidently come into too close contact with the yolk, hence the 

 lack of a lens and the duplicature of a part of the wall of the 

 optic cup. Or again, in figure 6 the cyclopean eye of the embryo 

 exhibits a very striking pecuHarity of another kind. Here the 

 eye is seen to be irregular in form, anteriorly it lacks the pupil 

 and is entirely surrounded by the pigment layer, while the lens 

 is seen to be on the posterolateral aspect of the eye. 



Besides the synophthahnic or cyclopean defect I have fre- 

 quently found embryos with a single eye in the usual lateral 

 position of the head (figs. 14 to 17) and of apparenth^ normal 



Fig. 13 Embryo with unilaterally defective head, one normal and one rudi- 

 mentary, eye, from acetone solution (.35 cc. gram molec. to 50 cc. sea-water) 

 eig;hteen days old. 



Fig. 14 Monophthalmia asymmetrica, from acetone solution (35 cc. gram 

 molec. to 50 cc. sea-water), nineteen days old. 



Fig. 15 Monophthalmia asymmetrica, from acetone solution, (35 cc. gram 

 molec. to 50 cc. sea-water) nineteen days old, m., mouth. 



