History of a transient nervous apparatus in certain Icbthyopsida. 41Ô 



Fig. 17. On the right a group of transient ganglion-cells projecting 

 towards the myotome, on the left a ganglion-cell engaged in spinning 

 a fibre as in Figs. 11 and 12. Embr. No. 143. Magnif. 225 X I- 



Fig. 18. A large group of transient ganglion-cells partly lying at 

 the apex of the cord and partly extending in a chain-like fashion to 

 the apex of the myotome. Embr. No. 81, 8 mm. Magnif. 225 X -f- 



Fig. .19. From the same embryo. The figure shows the extension 

 of transient nerve-fibres in this embryo. Magnif. as above. 



Fig. 20. From the same embryo. The commencement of the 

 spinning of a fibre by a central transient cell. Magnif. as in Fig. 18. 



Fig. 21. A section from an older embryo (No, 157, 100 somites). 

 On the right a fine nerve-fibre is seen passing from a central ganglion- 

 cell, while the corresponding fibre of the other side has a number of 

 transient ganglion-cells applied to it. Magnif. 225 X i- 



Fig. 22. The figure shows the arrangement of the central ganglion- 

 cells in a section from a 10 mm embryo (No. 410) treated with chrome- 

 osmic-acetic acid. On each side a transient sub-epiblastic nerve is seen, 

 the one on the right of the figure having two applied ganglion-cells in 

 its course. A more complete figure of the sections in the immediate 

 neighbourhood is given in Fig. 24, Magnif, 225 X f- 



Plate 23. 



Fig. 23. A combination of several sections. To show how far 

 the course of the two sub-epiblastic nerves figured could be traced. 

 Embryo No. 410. 



Fig. 24. A second combination from several sections of the same 

 embryo. To show the origin, nature of formation, and build of two 

 other sub-epiblastic nerves. The ganglion-cells on each side should be 

 noted, as well as their application end to end. The figure again shows 

 the furthest limits to which the nerves could be traced. See also 

 Fig, 22 and Fig. 24 a (plate 26). Magnif, 225 X I- 



Fig. 25. A third combination of three sections from the same 

 embryo. In the first section the nerve process extended from the 

 ganglion-cell to the tip of the myotome, and there was also a small 

 piece of nerve-fibre opposite the segmental duct. The second section 

 revealed a short piece just outside of and near the top of the myotome, 

 while in the third section the gap between the latter piece and that 

 opposite the segmental duct in the first section was completed and 

 filled-in by a long intact stretch of fibre reaching nearly the whole 

 length of the myotome. On the right of the figure a process of a 

 ganglion-cell touching the epiblast. Magnif. 225 X I- 



Fig. 26. Shows a transient ganglion-cell lying in the outer epi- 

 thelium of the muscle-plate and near the apex of the latter. No nerve 

 fibre connecting it in any way with other elements of the transient 

 system was detected. Embr. No. 343, 17 mm, about 133 somites. 

 Magnif. 500 X I- 



Zool. Jahrb. IX. Abth. f. Morph. 28 



