360 JOHN BEARD, 



backwards, and disappear about the region of the 3'l»t metamere" ^). 

 As stated there this only holds for those cells of the transient system 

 of Baja first developed. 



Reference may next be made to the figure (Fig. 89, plate 26) of 

 a portion of a median vertical section from an embryo (No. 220) of 



24 mm. This may also be compared with the as yet undescribed 

 figure (fig. 13, tab. 22) of Dohrn's memoir (No. 5). 



Both figures show very similar things, but probably Dohrn's 

 one relates to Seyllium or Pristiurus, at any rate this may be con- 

 cluded from the paucity of the ganglion-cells in the figure. 



In Fig. 89 an attempt has been made to render faithfully the 

 number of ganglion-cells met with in the particular section without 

 diagrammatically increasing or decreasing the total. Better than either 

 transverse or horizontal sections such a one as that here figured 

 illustrates the massing of the ganglion-cells in that region of the cord 

 in which they are most numerous. 



Reverting to the notes of series No. 201 it should be stated that 

 in this embryo the transient system exhibits no specially high degree 

 of development. Sub-epiblastic nerves were not noticed, except such 

 as had no great extension. Simple nerve-processes of ganglion-cells 

 are, however, fairly numerous. 



Another figure (Fig. 97, plate 27) from an embryo (No. 442, 



25 mm) treated with Flemming's reagent, perhaps furnishes a better 

 idea of the topography of the transient ganglion-cells as demonstrated 

 by horizontal sections. The total length figured is approximately 

 0,5 mm, and in that there are seen to be about 100 ganglion-cells, 

 leaving out of account others which lie more superficially or more 

 deeply. A smaller portion is drawn with greater accuracy in Fig. 91. 



Before proceeding to the consideration of another set of embryos, 

 Figs. 96 and 98 pi. 27, parts of horizontal sections of an embryo of 2H mm 

 (No. 529), may be briefly described. The first of these (Fig. 96) de- 

 picts a number of the centrally lying ganglion-cells, and also two 

 very curious nerve-gauglionic plexuses. As its main importance is, 

 however, to be viewed the circumstance that it proves the central 

 ganglion-cells to be in close communication and connection by means 

 of a mesh-work of processes. For the rest, the figure also demon- 

 strates how simple and primitive the axis-cylinder processes may be 

 by which groups of extra-medullary ganglion-cells communicate with 



1) No. 3, p. 193. 



