216 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
are proliferated from the region of encephalomere VI, the greatest pro- 
liferation occurring, however, as in the case of encephalomere V, in the 
posterior part of the encephalomere. No previous observer has stated 
that the ceils of the ganglionic Anlage of the ninth nerve are proliferated 
from encephalomere VI. However, that previous observers have seen 
the proliferation of cells from this encephalomere is possibly shown by 
the fact that both Shipley (87) and Kupffer (94) have found in Petro- 
myzon, between the Anlagen of the 7th and 9th nerves, a “weak 
primitive acusticus, which soon vanishes.” Hoffmann (94) stated that 
in Acanthias embryos with 32 to 35 somites, a new outgrowth appears 
between the facialis and the glossopharyngeus, which to all appearance 
is a rudimentary and early aborting segmental nerve. Although Hoft- 
mann published no figures, I infer from his description that this out- 
growth, or rudimentary nerve, is that portion of the neural ridge which 
is proliferated from the region of encephalomere VI. I am at least able 
to say positively that no other outgrowth of cells takes place just pos- 
terior to the Anlage of the acustico-facialis. In the phenomena pre- 
sented by this outgrowth Hoffmann finds the chief support for his 
contention that the Anlagen of cranial nerves arise as paired segmental 
outpocketings of the neural tube, corresponding to, or comparable with, 
the outgrowth of the eye vesicles. He figures diagrammatically the out- 
growth of the neural crest in the region of the glossopharyngeus Anlage 
as an outpocketing of the dorsal wall of the neural tube possessing a 
lumen continuous with that of the tube. At no time do I find evidence 
of a lumen between the neural-crest cells, although in later stages the 
nuclei in the VII and IX ganglionic Anlagen tend to take a peripheral 
position, 
At a stage with 26 or 27 somites (Plate 3, Fig. 12) the thalamic por- 
tion of the trigeminus Anlage is no longer continuous dorsally with the 
posterior portion of the Anlage, the cells of which come to lie in the 
region of constriction between midbrain and hindbrain. The thalamic 
portion extends from the constriction between primary forebrain and 
midbrain toward the eye vesicle, just behind which it unites with a line 
of cells, ectodermal in origin, which extends along the dorsal border of 
the eye close to the superficial ectoderm. Some of the cells of the 
trigeminus Anlage now extend into the mandibular arch, and have there 
come to surround the mandibular mesoderm. 
A displacement of the cells of the Anlage of the acustico-facialis and of 
the glossopharyngeus has begun at this stage. This is clearly to be ac- 
counted for by the invagination of the auditory epithelium, which is now 
