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



A comparison of comparable levels of the specific stages 

 described, for instance, a comparison of the section at the level 

 of the optic stalks in the 7 mm. stage with the section at about 

 the same level in the 9 mm. stage, confirms the general features 

 observable from fiat reconstructions and in addition shows 

 the following characteristics: 



(1) Both Gasserian and profundus increase markedly in com- 

 pactness and definiteness of boundary from early to late stages. 

 The proportion of cytoplasm to nuclei appears to decrease. 



(2) Mitotic figures or other evidence of growth by this 

 method are rare in both ganglia at any stage, although they 

 are numerous in surrounding structures. 



(3) The ganglion cells can always be distinguished from those 

 of the surrounding mesenchyme because of their pigmented 

 cytoplasm and small yolk granules, and small, quite uniformly 

 darkly staining nuclei. In the youngest stage large yolk 

 granules are sometimes seen in the ganglion, but in the older 

 stages there seems to be no evidence of the mingling of the 

 mesenchyme with either ganglionic mass, i. e., either profundus 

 or Gasserian, nor of the shelling off of ganglionic cells into 

 the surrounding mesenchyme. 



(4) The anterior end of profundus in the 6 mm. . and the 

 7 mm. stages lies close to a supra-orbital placode. 



(5) The ventro-lateral projection of the Gasserian is closely 

 associated with the first visceral pouch. 



The relation of the anterior part of profundus to the supra- 

 orbital placode is a very striking one. Until however the origin 

 of the profundus ganglion and of the lateral line system have 

 been described for this type, one is not justified in attempting 

 to explain the significance of this relation. The same may be 

 said for the relation of the ventro-lateral extension of the 

 Gasserian ganglion to the first visceral pouch. 



The Phylogenetic Relations of the Ramus Opthalmicus 



Profundus. 



In order to make clear the bearings of the results of this 

 ontogenetic study on the phylogenetic history of the profundus, 

 it will be necessary to summarize the relations of the profundus 

 ganglion and its nerves in the vertebrate phylogenetic series. 

 Table 2 is a synopsis of the conditions in great part as given 

 by AlHs '97. 



