PLATE 9 
Fig. 44 from an 8.8 mm. embryo shows the earliest trace of cells in the IX that 
would ordinarily be identified as placode. Succeeding series do not show it to be 
continuous and it differs from other placodes in having the ectodermic shelf extend 
mesially to the placodal cells. 
Fig. 45 from a 9.7 mm. embryo shows, in the IX, the earliest trace of the placode 
that can be followed continuously in later series up to the time of its detachment. 
Fig. 46 from a 10mm. embryoshows the ‘comma’ stage of [IX immediately after or 
during its detachment from the epidermis. The placode is not sharply differen- 
tiated from the general visceral, but includes at least all of the ventro-laterally 
projecting mass. The whole ganglion rests upon the ectodermic shelf. 
Fig. 47 from a 12.4 mm. embryo passes through the anterior end of the placodal 
“mass of cells of [IX and is almost surrounded by the general visceral cells. 
Fig. 48 from a 12.4 mm. embryo passes through the point where the lateral spur 
of placodal cells is present and the remainder of the placodal cells are only partially 
incorporated and occupy the ventral side of the ganglion. Fig. 48 lies three sec- 
tions back of fig. 47. ; 
Fig. 49 from a 10 mm. embryo shows the early stage of the epibranchial placode 
of the first branchial ganglion of X still attached to the ectoderm. 
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