428 MONTGOMERY. [Vol. XIII. 



In both species of Linens examined the oesophageal nerves 

 have four commissures, of which the fourth (last) is the largest, 

 and accordingly corresponds to the third of Cerebrahdus. The 

 commissures are more widely separated in Linens; otherwise 

 the oesophageal nerves have the same structure as in Cerebra- 

 tulus. 



VII. General Conclusions. 



1 . To the central nervous system of the nemerteans belong 

 the dorsal and ventral brain lobes, the lateral chords, the oeso- 

 phageal and proboscidean nerves, and the dorsal, unpaired, 

 longitudinal nerves. 



2. All ganglion cells are membraneless and unipolar, and 

 may be naturally divided into the four categories adopted by 

 Burger ('90b). 



3. In all the ganglion cells one or two (never more) spheri- 

 cal nucleoli are present, which are readily distinguishable from 

 the chromatin masses of the nucleus ; in the latter an achro- 

 matic reticulation is also present. I found only one cell with 

 two nuclei. 



4. The cytoplasm of the ganglion cells consists of staining, 

 more or less granular, but not fibrillar, spongioplasm, and un- 

 staining, homogeneous hyaloplasm, the latter usually in ex- 

 cess, especially in the distal portion of the cell. The cell is 

 bounded by a thin peripheral layer of fine-grained spongio- 

 plasm not in connection with the external neuroglia, and a 

 similar layer envelops the nucleus ; these probably represent 

 superficial alveolar layers, and the structure of the cytoplasm 

 a honeycombed meshwork, in the sense of Biitschli ('94). 



5. In the cytoplasm of cells III in Lineus, homogeneous, 

 deeply staining, more or less spherical bodies occur, which are 

 never numerous, and have no regular arrangement in the cell ; 

 to these bodies, which cannot be classed with the chromophilic 

 granules of other forms, the term chromophilic corpicscles has 

 been applied here. 



6. The axis-cylinder process is the same in all the ganglion 

 cells ; it represents a nerve tubule and not a " nerve fibril," 

 and is composed of : (i) the homogeneous, unstaining axis 



