History of a transient nervous apparatus in certain Ichthyopsida. 365 



Under a high magnification^) the same group is drawn again in 

 Fig. 60. The components are stained a rose colour with picrocarmine 

 in the section. As many cells as figured could be made out in the 

 clump, their outlines were anything but clear and the nuclei very 

 indistinct. Their characters can hardly be termed "ganglionic", but 

 there is an indefinable something about them, which stamps them as 

 degenerated ganglionic elements. 



The same combination drawing (Fig. 58) also marks at gl.c^ the 

 site of a true ganglion-cell. As can readily be observed, it lies not 

 far removed from the lateralis nerve, and is closely applied, as recon- 

 struction proves, to a transient nerve trunk. 



This cell is again figured under Zeiss' obj. F in Fig. 61 , and 

 the contrast of this actively living element of the transient system with 

 such a degenerated one as that figured in Fig. 59 (the position of 

 this is marked glc^ in Fig. 58) is very obvious, and need not be 

 dilated upon. 



The Fig. 61 is not an isolated instance of transient ganglion-cells 

 in the neighbourhood of the lateralis nerve; there are others in both 

 the embryos Nos. 229 and 237. 



The transient nerves are well represented in embryo No. 229, but 

 they are very difficult to follow; hence in writing the preliminary 

 paper many parts of them were overlooked. They always take their 

 origin either from centrally lying ganglion-cells or from groups of 

 such cells situated in the mesoderm. Except when ganglion-cells are 

 applied to them somewhere or other along their course, these nerves 

 always present similar characters. They are non-medullated nerve- 

 fibres, a very few of which make up a nerve, and nuclei are pretty 

 liberally applied to the trunk along its course (Figs. 63, 66 and 67, 

 plate 25). These appear to be more numerous when, as in Fig. 67, 

 the nerve is piercing the myotome. The usual course of sub-epi- 

 blastic nerves is shown in Figs. 62 and 65 of plate 25, and, under 

 higher magnification, portions of such nerves are depicted in Figs. 63, 

 66 and 67. Proceeding from central cells they pass outwards towards 

 the myotome, piercing this near its apex, and then, lying closely 

 applied to the outer side of the myotome and just beneath the epi- 

 blast, they continue their course, and can be traced in embryo No. 229 

 nearly as far ventralwards as the lateralis nerve. Their mode of 



1) A Leitz 2 mm pautachromatico oil immersion. The reduction 

 to two-thirds size in the process of lithography must be borne in mind. 



