234 BEATRICE WHITESIDE 
conditions and the first appearance of the calcareous contents. 
My paper begins with the stage at which Krause’s investigation 
(01) closes, in which the auditory vesicle is divided into utricu- 
lus and sacculus. At this time the ductus endolymphaticus is a 
small canal leading up from the sacculus, and the saccus is indi- 
cated by a small expansion at the distal end of the ductus. 
Before starting a report of my own investigation, I shall give 
a short account of previous observations on the development of 
the endolymphatic organs in the common frog, beginning with 
Krause (’01), who describes the formation of the ductus as follows. 
The auditory plate is formed from the inner layer of ectoderm on 
either side of the hind-brain. It consists of a single layer of long 
cylindrical cells which are longest in the middle of the plate, 
decrease in length toward its sides, and eventually pass into the 
very low cells of the outer layer of the ectoderm. First the 
dorsal side of this plate bends downwards and grows ventrally, 
losing its connection with the outer layer of the ectoderm. Thus 
the dorsal part of the auditory vesicle becomes marked off. This 
first formed part is the rudiment of the ductus endolymphaticus. 
Then the ventral:side follows, bulging outward at the same time. 
In this way the ductus is still more distinctly separated from the 
rest of the auditory vesicle and forced to the latter's median 
surface. 
There are, to my knowledge, only three other papers on this 
subject, namely, those of Villy (90), Poli (97), and Corning 
(99). All three investigators agree that the organ is formed in 
the above described manner. 
In all vertebrates the saccus endolymphaticus originates as 
an expansion of the distal part of the ductus. This structure 
is therefore a part of the inner ear and has no connection with the 
lymphatic spaces lying within the skull. Most authors confine 
themselves to this statement, and I know of only two detailed 
reports on the further development of this organ, the one by 
Rothig and Brugsch (’02), on the chick, the other by Streeter 
(16), on the human embryo. 
As regards the frog in particular, the papers of Coggi (’90) 
and Villy (90) are to be mentioned. Coggi gives a few details 
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