a4 
378 Charles R. Stockard. 
optic stalk, but the optic nerve fibers grow directly into the brain 
from the region of the eye cavity itself. 
It is interesting to find in this connection that Lewis (’70) 
describes in his experiments on tadpoles a strikingly similar 
course pursued by the nerves arising from some of the optic cups 
he had transplanted to various positions along the hind brain 
region of the embryos. He states that 
In a few of these somewhat irregular transplanted eyes the optic nerve 
takes a very curious course, passing across the cup cavity from the gang- 
lionic layer, through the pupil and then into the mesenchyme, ending 
there. In both of these experiments a small bundle of optic nerve fibers 
pierces the retina as far as the pigment layer. In transplanting these 
eyes the ganglionic layer was probably injured in such a way as to inter- 
fere with the normal path of the nerve fibers, and so they have prob- 
ably followed the path of least resistance through the pupil and out into 
the mesenchyme. 
Via. 138. A section of the embryo shown in figs. 5 and 6. The optic cups are 
joined dorsally and face the median plane of the head; a lens lies between them 
and is surrounded by loose cellular tissue instead of by the humor. 
Fic. 14. Section of the eyes in the embryo shown in fig. 4. The optic cups are 
not joined yet they face towards one another with their convex choroid surfaces 
pressed close against the head wall. The optic nerves run across what should be 
the humor chamber of the eyes and out through the wide pupils to form a perfect 
cross; the optic fibers then enter the brain floor. A lens lies between the eyes. 
