( 90) 



ture, as il presents itself in well-stained preparations of the nerve-cells 

 of the higher vertebrates (as for example in (lie splendid figures of 

 Donaggio). It seems thai the higher is the organisation of the animal, 

 and in consequence that of the nerve-cells, the finer and more regular 

 is the network of t lie neurofibrillae in the nerve-cells, (cf. Bochenek). 



The network of the neurofibrillae has no definite connection with the 

 protoplasma-reticulum. In preparations, preserved in a mixture of 

 Hermann's fluid and corrosive sublimate, and stained with iron- 

 haematoxylin, the protoplasma has a very fine granular or fibrillar 

 structure, and in the centre of many cells are shown curious diversely - 

 shaped differentiations that remind us of the pseudochromosomes 

 described by Heidenhain, and of the rings, described in the ganglion 

 cells of vertebrates (Teleostei, Kami). But it would take us too far, 

 to describe these details here at some length. 



2. An entirely different type of' cells we find in the nerve-cells 

 which form the large group of ganglion cells lying dorsally in the 

 foremost part of' the spinal cord just behind the brain ventricle, the 

 so-called oblongata, extending from the niveau of' the infundibular 

 organ till beyond the first pigmented eye-cells. It is characteristic of 

 .the peculiar difficulties, with which the investigation of the histology 

 of the nervous system of Branchiostoma is encumbered, that of' the 

 large number of authors, who have studied the subject, only Joseph 1 ) 

 two years ago gave a nearly accurate account of the structure 

 of' these cells. Even Heymans and van der Stricht in their very 

 elaborate study of the histology of the nervous system of Branchi- 

 ostoma, published in 1898, do not say a word about it, and only 

 in one of the many beautiful drawings, with which their paper is 

 illustrated, in two cells a slight indication of it is to be seen. Joseph 

 says of these cells, that they present at the surface a finely striated 

 border of' minute rods, only at the side of the cell turned towards 

 the surface of the animal, and underneath this striated border a 

 coarsely granular darkly staining protoplasm. The same structure 

 Joseph described in the cells lying close to the central canal in the 

 spinal cord, covered by a pigment-cap, and being supposed to be 

 light-percepling cells. On these grounds Joseph put forward the 

 suggestion, that the dorsal group of cells too consists of eye-cells, 

 light-percept ing cells, differing only from the cells of Hesse by the 

 absence of a pigmented cap-shaped cell. 



This far-reaching suggestion is, I think, not proved, nor even made 

 probable, by the facts. Even in the most carefully prepared sections 



l ) H. Joseph: Uebcr einige Zellstructuren im Zentralnervensystem von Amphioxus 

 Verh. d. Anatom. Gesellscliaft. Jena 1904. p. 1(3—26. 



