DEVELOPMENT OF EAR AND AUCESSORY ORGANS IN FROG. 531 
quickly than the remainder, so that it never becomes deeply 
constricted off. 
e. The Cochlea.—Under this heading I include the three 
pouches of the sacculus described by Hasse! and Retzius? as 
the lagena, the pars neglecta, and the pars basilaris. There 
"is very little of importance to note concerning them except 
the relative times at which they appear. ‘lhe lagena is the 
hindermost and largest of ‘the three. It first appears as 
a small pouch at the lower and inner angle of the vesicle, 
Opening into it at about the level of the anterior aperture of 
the posterior vertical canal (see fig. 8). It early acquires con- 
siderable size, and extends back some distance. As the peri- 
lymphatic spaces form, as described below, the inner wall of 
this pouch becomes thin and abuts against one of these canals, 
the part of the pouch concerned presenting a flattened appear- 
ance. The remaining parts of the cochlea develop simply as 
bulgings of the walls of the sacculus. The first of these to 
form is the anterior and upper one, which is situated close 
beneath the mouth of the recessus. This is called the pars 
neglecta. The pars basilaris is therefore the last part to appear. 
d. The Epithelium of the Auditory Vestibule.—In 
this section I propose to trace the formation of the patches of 
sensory epithelium in the various parts of the ear. 
When the lining of the invaginated auditory vesicle begins 
to differentiate, cells of two kinds may be distinguished— 
columnar and pavement. ‘The columnar cells are disposed ina 
tract running the length of the floor of the vesicle, and espe- 
cially well marked at the inner angle. This tract extends up 
the inner wall for a certain distance, and in the fore part it 
runs up the outer wall. The remainder of the vesicle is formed 
of a flattened epithelium. The columnar portion of the epithe- 
lium, however, divides and gives rise to all the sensory patches 
present in the adult ear, although at the time under considera- 
tion it 1s continuous. 
The sensory patches of the ear are eight in number. ‘Three 
: «Zeitschr. f. wiss. Zoologie,’ xviii, ‘ Das Gehororgan der Frésche.” 
2 « 1). Gehérorgan d. Wirbelthiere.” 
