2), G. W. BARTELMEZ 
ment. Unlike the preceding specimen (fig. 9b) or the following 
one (fig. 9d), this has the anlagen cut transversely (fig. 9c). 
Active evagination has begun and on one side there is a deep pit 
at the center of the primordium, which is, however, confined 
to the single 5u section here drawn. Figure 10 (op. sul.) shows 
the deepening optic sulcus as it appears in the twelve-somite 
embryo H 197. The optic portion is differentiated from the 
rest of the anlage as has been said and appears as a long narrow 
field measuring 60 x 200u with the suleus running through the 
middle. The optic anlage of the eleven-somite H637 is practi- 
cally identical in appearance with this one. 
Figure 9d was made from the ninth section of the eleven-somite 
embryo H392. The space separating the two neural folds here is 
the neural groove, the bottom of which is one-tenth of a millimeter 
caudalward in the series. The sulcus is cut obliquely, but is 
actually deeper than in any case we have considered. It will 
be noted that the optic evaginations are still directed ventrally. 
They correspond closely in position and extent to those of ‘Du 
Ga,’ in fact these two embryos are very similar in most respects. 
Our next stage is found in the fourteen-somite embryo ‘Pfst. 
IIV (Keibel u. Elze, ’08, Taf. 6), which is well known from the 
work of Low (’08) and others. This has the earliest optic anlage 
that has been described hitherto in man. It begins about 130u 
behind the rostral tip of the nervous system and is present in 
twenty-one of the 10u sections. Throughout this region the 
neural folds are still open. A section through the middle of the 
anlagen may be seen in figure 9e and a more caudal level appears 
in figure 2e. The striking change here is that the optic evagina- 
tions are now directed laterally toward the overlying ectoderm 
as a result of the rapid approximation of the neural folds. Ac- 
cording to Low, there is an area of contact between the young 
optic vesicle and the overlying ectoderm. Keibel und Elze 
describe the vesicle as ‘close’ to the ectoderm, Bach und See- 
felder (’14) intimate that there is no actual contact nor do Doc- 
tor Evans’ tracings show any. Certainly, there is no mesoderm 
between the two epithelia and in the immediately following 
stages the lateral side of the vesicle comes into close contact with 
