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



Plate V. 



Figure 29. A copy of a portion of a flat reconstruction by W. J. Kostir of a 

 Plethedon embryo 11.5 mm. in length. The scale at the top of the figure indicates 

 the number of sections 10 micra in thickness over which the plot extends. The 

 figures indicate the numbers of the sections, counted from the anterior end of the 

 body. 



This reconstruction shows the most fused embryonic condition of the trig- 

 eminal complex so far studied. The profundus portion is not distinct; the nerve 

 trunks are formed and the ganglion is over-lapped by the D. L. VII. X 66. 



Figure 30 is a flat reconstruction of the Gasserian, profundus and a part of 

 the D. L. VII of Plethedon gl. stage M, 9 mm. in length. This shows a well fused 

 condition of the Trigeminal complex and a single root, which is indicated by 

 dotted lines (Rt. Gass. G.). An outline of a longitudinal section of the head was 

 made on coordinate paper with a camera lucida. This outline was used as a hor- 

 izontal axis and guide in making the reconstructions of the transverse sections. 

 The same method was used for the reconstructions shown in Figs. 31 and 32. 

 The scale at the top of the figure indicates the number of sections 10 micra in 

 thickness over which the plot extends. The figures indicate the numbers of the 

 sections counted from the anterior end of the body. The levels of the sections 

 detailed in Figures 1 to 6 are given. X 50. 



Figure 31 is a flat reconstruction of the Gasserian and profundus ganglia and a 

 part of D. L. VII of Plethedon gl. stage G., 7 mm. in length. The roots of pro- 

 fundus and Gasserian are separate at this stage. A dotted line indicates the line 

 of contact of the profundus and Gasserian posterior to the root of profundus. 

 X 50. 



Figure 32 is a flat reconstruction of the Gasserian and profundus ganglia of 

 Plethedon gl. stage B., 6 mm. in length. The ganglia have no roots at this 

 stage. This shows the unfused condition of the profundus and the Gasserian and 

 the number of sections by which they are separated. The contact of the pro- 

 fundus with the ectoderm is shown (Ec. Con.). X 50. 



