214 G. W. BARTELMEZ 
Discussion—The otic primordia 
The findings in respect to the otic plate require little comment. 
Wilson (714) and Ingalls (’20) found it difficult to determine the 
limits of the plate in their two-to-three-somite specimens and this 
is true of all the earlier stages in its development. It is relatively 
more extensive shortly after it appears than it is later. There 
is at first an ill-defined thickening of the ectoderm opposite the 
second primary division of the hindbrain, but later while the 
ganglion is differentiating only the cells at the dorsal and rostral 
ends of the ectodermal area continue to elongate. The invagina- 
tion begins at about the time the neural folds are closing at 
this level. 
The history of the so-called acousticofacial ganglion has not 
been made out adequately in any mammal. It cannot be done 
in man until there is a complete series of well-preserved embryos 
available between fifteen- and twenty-five-somite stages. The 
conditions in this region of carnivore embryos seem to be quite 
similar to those in man. Weigner (’01) for the ferret and Schulte 
and Tilney (15) for the cat consider that the geniculate and ° 
acoustic ganglia arise from a common anlage. It remains to be 
seen whether, in mammals as in many other vertebrates, the 
otic plate contributes cells to the eighth ganglion. Certainly, 
such an addition cannot be great. As for the geniculate ganglion, 
it is certain in the human that part of it arises from the epi- 
branchial placode of the hyoid arch which is constantly present 
in fourteen-somite stages and later (ef. the findings of Giglio-Tos 
in his fifteen-somite specimen). This contribution from epibran- 
chial placodes has been well established for all cranial nerves 
in Ichthyopsida which have a gustatory component, largely 
through the work of Landacre and his students. In the case 
of Ameiurus, Landacre (’10) found that the entire ninth ganglion 
arises from such a placode, and in the adult of this fish the ninth 
appears to be a pure gustatory nerve. The evidence here is so 
clear-cut as to warrant the working hypothesis that in other 
vertebrates the gustatory ganglion cells of the seventh, ninth, 
and tenth cranial nerves arise from epibranchial placodes. The 
