362 JOHN BEARD, 



viz, a very fine 2 mm Pantachromatic by Leitz. It is a sketch of 

 a bipolar ganglion-cell (w.gl.c) having one process passing to the 

 central cells, whilst the other proceeds outwards iu the direction of 

 the myotome. Before getting there it terminates in a blunt rounded 

 end, and in the substance of the axis-cylinder at this point the nucleus 

 of what may be termed a nerve-forming cell is embedded. 



From embryo No. 219 (37,5 mm) Figs. 44 and 49 on plate 24, 

 and Fig. 101 on plate 28 are taken. 



Dealing with the latter figure first, the ganglion-cells iu the cord 

 are still in the condition ascribed to those of No. 209, that is to say 

 there are as yet no signs of degeneration. Indeed, what was said 

 concerning Fig. 36 holds ceteris paribus for the rest of Fig. 101, for 

 the two figures are exceedingly alike. 



Of the other two figures, Fig. 49 is intended to represent a portion 

 of a transient nerve-fibre (n.p) with three nuclei embedded upon it, 

 whilst Fig. 44 will be cited again subsequently as an interesting 

 example of the "degradation" of a bipolar ganglion-cell to the con- 

 dition of a nerve-forming cell. Fortunately the fibre, of whose nervous 

 nature no doubts could be entertained, could be drawn, as in the 

 figure, from one section without the necessity of reconstruction. The 

 nucleus in the middle would appear to have the nature of that of a 

 reduced ganglion-cell. This will be more obvious in the sequel, when 

 a series of figures shall have been compared together. 



From the series of horizontal sections of embryo 435 (33 mm) 

 Figs 82 (plate 26) and 100 (plate 27) are drawn. The first of these, 

 Fig. 82, serves as one proof out of many of the multipolar nature of 

 the transient ganglion-cells roofing in the cord. How many of these 

 processes are nervous and how many dendritic? Personally I incline 

 to a belief that several processes of one of these transient ganglion 

 cells may be nervous in nature. The apparatus is such a lowly or- 

 ganised form of nervous mechanism that one may not expect the 

 high specialisation of its component cells which characterises, for 

 example, ganglion- cells in the nervous system of the adult Raja. 



The other figure (Fig. 100, plate 27) reveals a clump of ganglion- 

 cells which projected from the highest level of the cord into the 

 mesoderm. On the one hand there was a nerve-root reaching into 

 the cord, and on the other a somewhat "dendritic" arrangement of 

 axis-cylinders proceeding from the ganglion cells and spreading out in 

 the mesoderm. Probably, however, there is no actual branching of 

 these axis-cylinders, and, if the complex were resolved into its com- 



