Dec, 191G] Profiindiis and Gasserian Ganglia in Plethodon 33 



small triangular part near the medulla and the other a large 

 distal part lying over the gill pocket, as in the 7 mm. stage. 

 These two portions are connected by pigmented cytoplasm. 



At the level of figure 27, Plate IV^, almost at the posterior 

 end of the optic vesicle the Gasserian is restricted to a few cells 

 over the first gill pouch. The supra-orbital lateral line placode 

 (PI) is large and shows a radial arrangement of cells. For a few 

 sections posterior to Figure 27, the cells of the Gasserian are 

 mingled with the ectoderm at the apex of the first gill pouch. 

 They are apparently continuous with the inner layer of the 

 ectoderm lateral to the endodermal pouch. 



The Fusion of the Profundus and Gasserian Ganglia. 



The form relations of the profundus and Gasserian ganglia 

 in the specific stages described above furnish abundant evidence 

 for the fusion intact of these ganglia. However, in order to 

 determine whether there is other evidence bearing on this 

 question aside from that of form relation, a count of the nuclei 

 in the ganglia was made according to the principle stated on 

 page 27. 



Table 1. Showing the number of nuclei in the profundus 

 and Gasserian ganglia before and after fusion. 



Stage Length No. of Nuclei 



B () mm. Gass. 480, Prof. 570. 



G 7 mm. Trigeminal Complex 1330 



M 9 mm. Trigeminal Complex 1350. 



In the 6 mm. stage the Gasserian has only 480 nuclei, at 

 9 mm. the trigeminal complex has 1350. It is obvious that 

 this increase in number of nuclei is due mainly to the fusion 

 of the profundus portion with the Gasserian. The number of 

 nuclei in the trigeminal complex in the 9 mm. stage is a little 

 more than the sum of the number of nuclei in the gasserian and 

 profundus at the earlier stage where the two ganglia are separate. 



The increase in number of nuclei from 1050, the sum of 

 the nuclei of profundus and Gasserian in the 6 mm. stage before 

 fusion, to 1350 in the 9 mm. stage may be partly accounted for 

 by mitosis. Although the mitotic figures in the ganglia at 

 any stage are extremely scarce, the maximum is 10 in the 

 ganglion at any one stage. The difference is 200 nuclei. At the 

 maximum rate of 10 for every stage between 6 mm. and the 9 mm. 



