THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS ot 
surrounded by general visceral cells. After growing mesially 
and coming into contact with the general visceral ganglion 
at about the age of 94 to 100 hours, it becomes detached 
from the ectoderm when the embryo is somewhat less than 10 mm. 
in length. At the point of detachment there is left a cell mass 
which extends backward to the region of the ear. 
Preceding and for a long time after detachment, the placodal 
cells are sharply differentiated from the remainder of the genic- 
ulate cells. As late as the 44 mm. stage and probably as late 
as the 152 mm. stage some of the placodal cells are differentiated 
by their small size and intense dark color. The number is con- 
stantly reduced, however, and similar small dark staining cells 
can be detected in other ganglia particularly the Gasserian, so 
that the fact that one can trace the history of these cells to so 
late a period is probably due to their late differentiation into 
normal ganglion cells. 
Just how much of the geniculate ganglion at any stage after 
the detachment of the placode and after the metamorphosis 
of the small placodal cells into normal ganglion cells, may be 
general visceral and how much may be special visceral cannot 
be determined, but the late differentiation of these placodal cells 
enables one to locate them and follow their history before meta- 
morphosis much more completely than in any type described. 
The relation of the early stage of this placode to the dorso- 
lateral sensory lines needs a more careful study than can be given 
the question in connection with the later history of the placodes. 
The presence of definite sensory lines resembling those of the sea 
bass (Wilson, 791) shows that the lateral line system, at least in 
its earlier stages, resembles Serranus much more closely than 
Ameiurus, but whether these sensory lines are continuous with 
the anterior end of the auditory thickening (preauditory placode 
of Ameiurus, Landacre, ’10) or not must be taken up separately. 
The presence of epidermal thickenings or sensory lines, lying at 
the same level as the preauditory placode or dorso-lateral sensory 
line, but not identical with it, as a study of the epibranchial 
placodes of the IX and X nerves shows, emphasizes the necessity 
of exercising caution in order not to confuse these dorso-lateral 
