366 H. M. BERNARD. 
“primary optic vesicle ” reproduces the retina and specialised 
chromatophoral layer of the eye when it was at the stage shown 
in Diagram II. This would account for the fact that the 
lens, though it appeared, as I think, in the epidermal stage of 
the eye, does not appear ontogenetically with the primary 
optic vesicle, but has to develop separately. 
Some confirmation of this view will be found if we compare 
the shape of the optic cup with the retina at the first hypo- 
thetical stage. The primary optic vesicle never apparently 
forms a true cup; it is far more spoon- or ladle-shaped, the 
sides gradually folding up over the handle or stalk. The 
stalk itself tends to fold, and where the sides of the spoon meet, 
just over the handle, the choroid fissure arises. This is an 
almost exact reproduction of the retina shown in Diagram II. 
As the primitive retina expanded, the optic nerve entering from 
the edge may have been wide and fan-like. As then the retina 
bulged deeper into the body, and its sides folded steeply up, 
the optic nerve would also fold with it near its junction with 
the spoon-shaped retina. This folding would be more marked 
if the point where the nerve joined the retina left the level of 
the skin and travelled inwards towards the base of the in- 
vagination. I claim, therefore, that we have here direct em- 
bryological evidence of the former existence of a ladle-shaped 
retina almost exactly corresponding with that sketched in 
Diagram II, i.e. without a lens in organic connection with it. 
The ontogenetic development of the lens takes place, as is 
well known, by an invagination of the ectoderm ; this obviously 
does not and cannot repeat the evolutionary process as depicted 
in the diagrams. It is, perhaps, probable that the embryo- 
logical invagination which forms the lens may be some faint 
attempt to repeat the invagination shown in Diagram III. 
Any way this method of lens formation would clearly have to 
be adaptive if the account above given of the origin of the 
“primary optic vesicle”’ is approximately correct. As far as 
I can remember, nothing similar to this suggested complica- 
tion has been recorded, although if we knew enough we should 
probably find it to have been very common. We have the 
