286 OTT. [Vol. VII. 



the sections to be finely granular and to have small round or 

 oval, finely granular nuclei. The nuclei are from .3 to 1.75 /* 

 in diameter. The structure of these amoeboid cells is finely pre- 

 served in worms which have been fixed in either chrom-osmic- 

 acetic acid or corrosive sublimate. When a corrosive sublimate 

 section is stained with hsematoxylin, the protoplasm of the cells 

 takes a light purple stain (Fig. 17). In a section of a worm 

 fixed in chrom-osmic-acetic acid and stained in alum carmine the 

 nuclei of the amoeboid cells took a dark purple red stain, while 

 the cell contents took a light red stain (Fig. 19). 



The commissure (Figs. 17 and 18) connecting the two lobes 

 is seen to be made up of fibres and to be free from an investing 

 layer of cells. It is cylindrical and has a diameter of 20 yu,. 



In a cross-section of the commissure taken from a point mid- 

 way between the ganglia it has the appearance of being made up 

 of a very fine network of fibres enclosing round or polygonal 

 spaces (Figs. 17 and 19). This network is more pronounced 

 toward the middle of the commissure. The spaces are filled 

 with a very finely granular substance. Toward the ventral side 

 of the commissure large, light-colored, irregular shaped spaces 

 may be seen, which appear different in character from the polyg- 

 onal spaces in the centre of the commissure (Fig. 17, SJ). 



In cross-sections of a worm where a longitudinal section of 

 the commissure is obtained this same network is seen to be 

 present. In these sections the network is seen to enclose long, 

 narrow spaces rather than the circular or polygonal spaces seen 

 in the cross-sections. The greatest length of these spaces is 

 parallel to the length of the commissure. The large clear spaces 

 which were seen in the cross-sections are also seen toward the 

 ventral side of the longitudinal sections of the commissure. 

 Here they appear as long, narrow clear spaces (Fig. 18, 5.'). The 

 network is much more pronounced toward the point midway 

 between the lobes of the brain. At the lobes the strands cease 

 to form a network and run parallel to one another into the 

 lobes (Fig. 18, Fi). 



In sections of the worm which had been treated by Kolliker's 

 silver nitrate method (Fig. 19) the branched cells and the fibres 

 of the commissure took a dark brown stain, while the material 

 between the fibres was colored a light green. 



Nerves. — In the living worm which has been stained with 



