294 Charles R. Stockard 



The second type of optic defect caused by magnesium is a 

 new monstrosity and may be termed Monstrum monophthalmicum 

 asymmetricum, the monster with one asymmetrical eye. It has 

 only one perfect eye which represents one of the normal pair and 

 occupies the usual lateral position. This eye is in all cases perfect 

 while its mate may be indicated by either a small eye, by a mere 

 cellular mass representing an optic cup, or all indications of the 

 second optic cup may be wanting. (See Fig. 2.) This peculiar 

 one-eyed condition exists in many of the embryos in the magnesium 

 solutions. Had such a defect resulted from a mechanical opera- 

 tion, it would probably have been interpreted to mean that one 

 eye anlage was injured and the other not. With the solutions, 

 however, we get a clear case of the gradual dropping out of one 

 eye by comparing different individuals, and here as in cyclopia 

 the defect is present from the earliest appearance of the eye, and 

 is not due to a gradual degeneration, or arrest during develop- 

 ment. A study of sections of these embryos makes the conditions 

 clearer. 



a The Living Cyclopean Embryos from the First Indication of 

 the Defect to the Time of Hatching 



The optic vesicles appear in most eggs when about thirty hours 

 old; at this time the blastopore is just closing and the embryo is 

 well mapped out on the embryonic shield. Many attempts were 

 made to select cyclopean individuals at this stage but it could not 

 be done with a great degree of certainty, since some embryos 

 are always slow in giving off the optic vesicles and these at times 

 appear to have only one, but when examined some hours later 

 are found to be normal. A number of eggs were selected, how- 

 ever, at thirty hours old which proved to be cyclopean on later 

 examination. 



At about forty hours the defect is plainly detectable so that one 

 may arrange the eggs very accurately into two groups, the cyclo- 

 pean individuals and the normal. After such a separation, none 

 of the normal embryos ever exhibited the cyclopean defect in later 

 stages, although kept in Mg solutions. A number of such tests 

 as this in connection with the study of sections convinced me that 



