224 G. W. BARTELMEZ 
have presented strong evidence that this is so for the cat. On 
the basis of a complete series of models, they have described an 
absolute decrease in the size of the optic vesicle during the proc- 
ess of its separation from the brain and the formation of the 
stalk. It is not unlikely that the same conditions obtain in 
man. With the rapid enlargement of the optic ventricle the 
wall of the vesicle becomes thinner, whereas the diencephalic 
wall dorsal to it remains as thick as before. 
These conditions emphasize another significant fact. The 
optic primordium is laterally placed, but not in direct continuity 
with the future skin ectoderm. The future roof plate and part 
of the alar plate intervene. This strongly supports the theory 
that the vertebrate eye originated within the central nervous 
system. Other evidence for this has been convincingly pre- 
sented by Parker (’08). If the optic vesicle and its derivatives 
were lateral ectoderm incorporated into the neural plate, it 
would be necessary to assume that the hiatus left by the separa- 
tion of the vesicle was filled by an ingrowth of neural epithelium 
from either side. Such ingrowth should be manifest first as a 
notch in the side of the anterior neuropore or later as a suture. 
There is no evidence of such conditions in the pertinent stages 
we have examined, and we may confidently say that mammalian 
ontogeny offers no support for the theory of the peripheral origin 
of the eye. 
The anatomical evidence here, as in vertebrates generally, 
indicates that the optic primordia are lateral in position from the 
outset. The experimental evidence which has been well sum- 
marized by Mall (’19) is conflicting. The experiments of Stock- 
ard on Amblystoma (’14) are the most complete. In order to 
substantiate his theory of cyclopia, this investigator set out to 
prove that the earliest optic anlagen are median in position. 
In most of the embryos which survived the removal of the middle 
third of the rostral end of the neural plate the optic vesicles were 
subsequently lacking, whereas they were usually present when 
lateral moieties were extirpated. Stockard was convinced that 
the evidence demonstrated the existence of a median origin of 
the two subsequently lateral vesicles. It is possible that he did 
