212 G. W. BARTELMEZ 
apparatus to be the first cytoplasmic differentiation which 
appears in the histogenesis of the neuroblast. 
The otic pit in the next two embryos is no further advanced 
in development than in that just described. In both it is shallow, 
in the eleven-somite H3892 confined to the rostral end of the 
plate. The differentiation of the ganglion from the neural fold 
is complete histologically in H 197 (fig. 8) and figure 6 illustrates 
a slightly later stage in transverse section. In the fourteen- 
somite New York University embryo (Wallin) a greater por- 
tion of the plate is invaginating, as may be seen in figure 2d on 
the right (ot. pl.). The ganglion appears in this section and in 
the one shown in figure 9c. It is this which Wallin (713) inter- 
preted as the trigeminal ganglion, for he failed to recognize the 
otic plate. In Pfannenstiel III (fourteen somites) the otic pit 
has deepened and lies somewhat ventral of the center of the plate. 
The appearance in section may be seen in figures 2e and 9e; 
in the former the rostral end of the plate and the ganglion are 
shown on the left, while on the right the plane of section passes 
behind the ganglion. The section shown in figure Qe lies still 
further caudad and exhibits the progress made by the otic invag- 
ination in this embryo. Ectoderm and neural tube are per- 
fectly distinct in both sections and were continuous across the 
midline in life, as is obvious from the study of a model constructed 
at a magnification of 200 diameters. The statement in the 
Normentafel indicates that Keibel and Elze (’08) also considered 
the neural tube closed in this region. Low (08), however, 
was misled by the artificial breaking of the ectoderm and separa- 
tion of the neural folds which extends far back into the region of 
the somites. Such cracks can be avoided, even in freshly pre- 
served embryos, only by the most scrupulous care in dehydra- 
tion and clearing if the material is to be imbedded in paraffin. 
The otic plate of the fourteen-somite embryo H8 presents an 
intermediate stage between the last specimen and that shown in 
figure 2f. The whole plate is invaginating, but the pit is not so 
deep as it is in the sixteen-somite Mall embryo there figured. 
The marked increase in the thickness of the otic epithelium will 
be noted in this ease. In both embryos the ganglion is almost 
