( 88 ) 



The axon of the colossal nerve-cells lias a somewhat different 

 structure. As I described in my former paper '), the colossal nerve- 

 fibres contain a great number of closely set exceedingly line separate 

 fibrillae, which in well-preserved preparations are distributed regularly 



through the whole extent of the fibre. There where the axon enters 

 the cell, this bundle of neurofibrillae may lie followed some way 

 into the cell-body ; we see the fibres describe a curve or vortex 

 around the nucleus, and then the thin fibres melt into the somewhat 

 coarser network of the neurofibrillae described above. 



The smaller, mediumsized and smallest nerve-cells of Branchiostoma, 

 such as those that are drawn in figg. 4, 5 and 6, at the same scale 

 as the cell figured in tig. 1, show the same arrangement of the 

 neurofibrillae as the colossal nerve-cells, viz. a regular network, the 

 meshes elongated there where a dendrite or axon leaves the cell, 

 more or less rounded in the centre of the cell-body. The subperi- 

 pheral zone with finer meshes and coarser fibrillae I could not. find 

 here; the network seemed everywhere to be regular throughout the 

 cell-body. In tig. -la and 4/; two sections through the same medium- 

 sized nerve-cell are drawn. In fig. 4// the nucleus is to be seen, and 

 on it a very regular network of neurofibrillae, with only one layer 

 of meshes, and therefore giving a very clear idea of the regularity 

 of the network. This section passes through the centre of the cell- 

 bod v. Fig. -if' shows the peripheral part of the same cell. The 

 meshes are here more elongated in the direction of the processus, 

 and in the network some fibrillae are coarser and more darkly 

 stained; all of' these run in the direction of the dendrite and leave 

 the cell-body there; inside the cell they form part of the general 

 network; in the dendrite they run more or less parallel to each other 

 and do not anastomose any more (see page 2). The same features 

 are to be seen very clearly in fig. 6, showing the neurofibrillar 

 structure of another mediumsized nerve-cell lying somewhat more 

 cephalad in the spinal cord. 



In fig. 5 is drawn a very small ganglion cell (magnified to the 

 same scale as the foregoing figures). Here too the network of the 

 neurofibrillae is easily to be seen and the meshes are of about the 

 same size as in the mediumsized nerve-cells described above, though 

 smaller than in (he colossal ganglion cells. 



Fusiform cells, in which the neurofibrillae simply pass through 

 the cell-body from one processus to the other without interruption, 

 as I described them in my former paper, I was not able to find in 



l ) These proceedings. Meeting of Oct. 25, 1902. 



