4 1 8 MONTG OMER Y. - [Vol. X 1 1 1 . 



to the ganglion cells themselves than to the cells of the 

 neurilemma (cf. Rohde, '90b). 



I have ('97) found that the neuroglia of the central nervous 

 system occurs in two or three modifications, according to struc- 

 tural differences: thus (i) the "outer neuroglia," which is 

 situated between outer and inner neurilemma, and (2) the 

 " inner neuroglia," in and around the fibrous core, may be dis- 

 tinguished in all nemertean genera; while in a few genera the 

 outer neuroglia may be subdivided into (a) the outer neuroglia 

 of the brain lobes, characterized by the presence of pigment, 

 and (b) the outer neuroglia of the lateral nerve chords, in which 

 pigment is absent. 



The membraneless, multipolar cells (Figs. 35 a-c, 40, Ngl. C.) 

 of the outer neuroglia, which are situated between the outer 

 and inner neurilemma of the brain and lateral chords, possess 

 long, fine, branching fibres which produce loose fibrous sheaths 

 around each of the ganglion cells of the types III and IV. In 

 the Figs. 3-16, 19, 21, 23, 27-29, 32 the fibres alone of the 

 sheaths (J^gl-) are reproduced, the cells from which they arise, 

 and which usually are more peripherally situated, having been 

 figured in my preceding paper (/. c). Burger ('90b) first 

 described these fibrous sheaths of the ganglion cells ; but he 

 had overlooked the more important fact that they are continued 

 along the nerve tubules also, producing an outer connective-tissue 

 sheath of the latter, which is fully comparable to the sheath 

 of Schwann (" Schwann'sche Scheide ") of, e.g., the vertebrate 

 axis cylinder, and for which the same term may be applied. 

 The number of fibres composing the sheath of the ganglion 

 cell is greatest and they are most loosely arranged around the 

 enlarged proximal portion of the cell (Figs. 3-8, 10-13, 19, 21, 

 23, 27-29, Ngl.). Towards the distal pole of the cell — the 

 point of origin of the nerve tubule — the number of enveloping 

 neuroglia fibres diminishes, and they commence to place them- 

 selves much closer to this portion of the cell. Finally, on each 

 side of the proximal portion of a nerve tubule, as seen on a 

 thin longitudinal section, one neuroglia fibre may be seen, and 

 can be traced to one of the fibres forming the fibrous sheath of 

 the ganglion cell. Thus the nerve tubule is enveloped by a 



