340 The Ohio Journal of Science [Vol. XVI, No. 8, 



The placodal thickening of the ectoderm is not so marked as 

 in VII, but the irregular arrangement of the cells, the presence 

 of mitotic figures and the tendency to lamellation of the placodal 

 mass (Fig. 14 and 15) are evidences of the integrity of the mass, 

 which is cjuite distinct from the lateralis placode and, toward 

 the posterior end of the ganglion, from the gill cleft thickenings 

 also. The outline of the general visceral portion of the ganglion 

 is maintained for several sections posterior to the point of con- 

 tact (Fig. 10) with the placodal mass, and the boundary line 

 between this and the placodal m.ass is quite distinct and intact 

 at some points (Fig. 10, 11, 12 and 15). 



In the mass of contributed cells, as well as in the placode, 

 there are numerous mitotic figures and there is, in every sec- 

 tion, a large group of undifferentiated cells (Fig. 11 to 15), lying 

 near the ectoderm, except near the anterior extremity of the 

 ganglion. Mesial to this mass is an area of cells with much 

 smaller, dark, granular nuclei, representing a stage of incom- 

 plete metamorphosis (Fig. 10 to 16, S. V. VII). The boundary 

 between this and the general visceral mass is quite abrupt and 

 distinct in most sections, but in some there is evidence of fusion 

 with the latter mass (Fig. 13). These facts are presented as 

 -evidences of the active state of proliferation and metamorphosis. 



The process of contribution to the ganglion does not persist 

 posterior to the point of disappearance of the general visceral 

 portion, though the placode persists several sections posterior 

 to both. 



It will be seen from these conditions, that Gang. IX presents 

 a much less mature condition than Gang. VII, which is to be 

 expected from the evidences already presented (Tables I and II). 



Gang. X. 



The main mass of the ganglion does not come into contact 

 with the ectoderm except at the extreme posterior extremity; 

 instead, it gives off four branchial ganglionic masses which 

 extend ventro-lateral something after the manner of the fingers 

 of a hand, and come into contact with the ectoderm of the 

 third, fourth, fifth and sixth gill bars respectively. The length 

 of each branchial division is measured from the point of its 

 complete separation from the main ganglionic mass. 



