294 TOKUYASU KUDO 
pocket-shaped olfactory pit is deep and the oral sinus deeply 
cleft. Fixation: formol-aleohol. Stain: alcoholic borax car- 
mine. Sections 15y in thickness cut frontally through head and 
entire body. The antero-posterior diameter of the auditory 
vesicle is calculated to be 0.48 mm., since it runs through 32 
sections. 
The auditory vesicle has at this stage undergone considerable 
development. The pars superior and the pars inferior are dis- 
tinetly separated. The anterior and the posterior semicircular 
canals are now completely constricted off; but this is not the case 
with the lateral canal; i.e., this canal is not yet independent of, 
but still broadly in communication with the main lumen of the 
vesicle. The pars inferior is well differentiated and possesses an 
elongated oval swelling on the ventro-medial wall of the vesicle. 
The ductus endolymphaticus appears as a long slender tube. 
In correspondence with the external change in form the epi- 
thelial lining is also well differentiated. The anterior canal, 
which is flattened in a medio-lateral (partly dorso-ventral) 
direction, widens out at its anterior end into an ampulla, and the 
crista acustica anterior is here represented by high epithelium 
which is continuous, without any decrease in thickness, with the 
macula utriculi. The same holds true for the crista lateralis, the 
epithelium of which is somewhat lower than that of the anterior 
crista. The medial and ventral walls of the utriculus are made 
up of especially high stratified epithelium, which, bending 
upon itself at the entrance of the pars inferior, passes over into 
this without any sharp boundary line. The tallest epithelium 
of the medial wall decreases somewhat in thickness as it passes 
over into the medial wall of the endolymphatic duct. The 
flattened lateral wall of the utriculus presents no points of espe- 
cial interest. The crista posterior has moved back some distance 
and appears as a thickened zone of cells in several layers at the 
ventro-medial portion of the semicircular canal. 
Stage 3 (fig. 3) The embryo consists of about 23 coils. 
On the surface of the body striations are observed. which 
are transverse on the ventral and crossed on the dorsal surface. 
Fixation: Corrosive-acetic. Stain: alcoholic borax, carmine. 
