388 Charles R. Stockard. 
If eggs be placed in Mg solutions five hours after fertilization, 
when in the sixteen or thirty-two-cell stage, an almost equally 
large number of cyclopean individuals will occur. The same is 
true when they are subjected to the solutions after having devel- 
oped in pure sea-water for seven and one quarter hours and reached 
the sixty-four or higher cell stages. 
Eggs that have developed eleven hours in pure sea-water and 
are in the early periblast stage with a somewhat flattened blast- 
odermic cap, may be put into Mg solutions and caused to form 
cyclopean monsters. The percentage of cyclopean embryos 
arising from eggs treated at this late period is small, yet even after 
developing for fifteen hours in pure sea-water some eggs may be 
induced to form cyclopean monsters by treatment with MgCl, in 
sea-water solutions. 
Eggs that were older than this before being introduced into the 
solutions failed to respond, all developing into ordinary two- 
eyed individuals. This is due to the fact that a considerable 
amount of time is necessary for the Mg to act-upon the body sub- 
stances of the early embryo and prevent normal eye developnfent. 
The optic vesicles begin to push out from the brain: before the 
thirtieth hour in development. Thus, after the first six or seven 
hours, the longer the eggs have been allowed to develop naturally 
the smaller the proportion of cyclopean individuals that may be 
artificially induced. After fifteen hours no embryo will be so 
affected, since an insufficient amount of time exists for the Mg to 
act on the eye anlagen. 
The solutions are effective up to a stage in development pre- 
ceding the formation of the germ ring and embryonic shield, and 
the action of the Mg on the eye anlagen probably takes place 
while the embryonic shield and outline of the embryo are forming. 
There can be no further doubt that cyclopean monsters are 
caused by the action of a strange environment on the developing 
fish embryos. With such evidence at hand it is also highly 
probable that mammalian cyclops are due to the action of external 
influences on the embryo and not to an abnormal germinal tend- 
ency. 
