32 The Ohio Journal of Science [Vol. XVII, No. 2, 



Description of the 6 mm. stage. 



The profundus ganglion is in the 6 mm. stage a loose mass 

 extending for about one-fifth its length anterior to the optic 

 vesicle and for four-fifths of its length is in contact with the 

 lateral ectoderm. The Gasserian at this stage is hard to define. 

 It has no root entering the medulla, but lies close to it. A 

 ventro-lateral extension projects to the region of the first 

 visceral pouch. At this stage the Gasserian and the profundus 

 are isolated from one another by a distance of three-eighths the 

 length of profundus, as may be seen in the fiat reconstruction 

 of this stage. (Fig. 32). 



The anterior end of the profundus ganglion lies in the region 

 of the fore brain just anterior to the optic vesicle. Near its 

 anterior end it consists of a loose mass of pigmented cells 

 attached to the ectoderm (Fig. 17, Prof. G.). 



The anterior portion of the ganglion lies in contact with 

 the ectoderm throughout most of its dorso-ventral diameter. 

 The greater part of this contact is immediately anterior to 

 the supra-orbital lateral line placode. This contact continues 

 to a point just anterior to the crystalline lens invagination. 

 Posterior to its loss of connection with the ectoderm the pro- 

 fundus becomes very indefinite. There are only a few nuclei 

 and these are separated from each other by cytoplasm and yolk 

 granules (Fig. 21). The profundus retains its position dorsal 

 to the optic vesicle until it drops out. At the level of the open 

 optic stalks no trace of a ganglionic mass is found. None 

 appears until the level of the anterior end of the Gasserian. 

 (Fig. 23-24 and Fig. 32, Sec. 76). This mass consists of a 

 few ganglion cells lying between the medulla and the ectoderm 

 just posterior to the open optic stalks (Fig. 24, Gass. G.). In 

 this group the ganglion cells have many cytoplasmic processes 

 and large yolk granules are mingled with them. For the next 

 ten or more sections the Gasserian ganglion is an irregular 

 triangular mass with its base in contact with the lateral part of 

 the medulla and its apex extending ventro-laterally to the 

 region of the first gill pouch. . 



At the level of figure 25 and figure 32 the Gasserian 

 (Gass. G.) is diffuse and has many strands of cytoplasm running 

 parallel to the long axis of the ganglion. A few sections posterior 

 to this point the Gasserian has two nucleated portions, one a 



