THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 29 
and ectoderm is not broken but at least half of this is formed of 
ectoderm and the ectodermic cells at the base of the proliferated 
mass are in active mitosis. 
In fig. 42 the endodermic pocket has withdrawn from the ecto- 
derm and the placodal mass projects freely into the mesoderm. 
One section posterior to this point the placodal mass is shorter 
and posterior to this is present as a slight ridge in the ectoderm. 
The condition just described, i.e., a thin flat placodal prolifera- 
tion of cells closely apposed on its anterior surface to the posterior 
wall of the hyoid gill pocket and usually extending through not 
more than four sections, is so constant that it is unnecessary 
to follow it in detail further than to give sections through the 
placode at its maximum size. Between the 7.3 mm. stage and 
the 8 mm. stage the general visceral portion of the VII has grown 
forward as shown in fig. 42 until it lies upon the dorsal surface 
of the posterior end of the hyoid gill pocket. This change in 
position of the anterior end of the ganglion carries the ganglion 
anterior to the point at which the placode originates; so that 
the placodal cells are added in such a manner that they work 
their way into the general visceral mass or are surrounded by 
the visceral cells; at any rate they are incorporated into the gen- 
eral visceral ganglion. 
In the 8.3 mm. stage (fig. 43), both the placode and the anterior 
end of the general visceral VII have increased in size. ‘The gen- 
eral visceral ganglion is irregular in outline and it is difficult in 
this particular series to tell how much of the complex is placodal. 
Mitotic figures are numerous both in the ganglion and in the 
placode. The dorso-lateral VII ganglion is present in fig. 43 
but the section is taken just anterior to the ventro-lateral VII. 
The changes in the placode, aside from its darker color, are 
almost imperceptible between the 8.3 mm. stage and the 9.5 
mm. stage (figs. 32 and 33). The general visceral portion of the 
geniculate, however, becomes more definite in outline and com- 
pared with the placodal portion of the ganglion, is much lighter 
in color and the cells are larger and more loosely arranged. Be- 
tween the 9.5 mm. stage and the 10 mm. stage which has been 
fully described, the placode becomes completely detached from 
