176 PATTEN. [Vot. II. 
p.n.f. primitive nerve fibres. z.z.¢. tongue of inverted cells. 
rd. rods. tm. tentorium. 
rd.' & rd.'! rods of primary and second- v.#. vertical nerve fibres. 
ary cells of the retinophorz. v.r. vertical retina. 
rn. retinidium. x. dark nuclei in young eyes. 
s. segments of nerve chord. y. yolk. 
s.o. segments of optic plate. y.c. yolk cells. 
s.o0.g. stalk of optic ganglion. z. first cephalic invagination. 
s.r.c. small retinal cells. z. second cephalic invagination. 
s. rd. small rods. _ I-10. sense organs of the eyes. 
z1-3 tentorium. x.y. upper edge of eye III. 
w38 terge. 
