318 rnivcrsitij of California Publications in Zoology [Vol. 11 



found also the significant thickening at its four sensory bulbs 

 from which Linko (1900) traced branches to the eye. The Hert- 

 wigs (1878) state that the two rings probably have different func- 

 tions; that the upper controls the sense organs while the other 

 gives off nerves to the muscular parts or motor organs. They 

 explain this difference from the fact that the motor organs lie 

 on the under side of the protecting velum while the sense organs 

 are on the upper side where they come in constant contact with 

 their surroimdings. In Polyorchis the two nerve rings (pi. 14, 

 fig. 5, n. >'., 1 and 2) are found. The lower nerve ring is the 

 larger, being composed of a bunch of nerve cells with their long 

 axes parallel to the rim of the bell. The cross-section of these 

 cells is shown at n. r. 2. The upper nerve ring consists of only 

 a few rows of cells arranged in one layer along the basal mem- 

 brane {n.r. 1). These are much larger than those of the lower 

 and contain very large nuclei. All the cells observed of both 

 rings were bipolar. 



Plate 15 shows isolated nerve cells, from the eye and adjoining 

 base of the tentacle, obtained from the macerated preparations. 

 Several types of nerve cells were thus found which were almost 

 impossible to observe in sections. No definite arrangement of 

 these cells was found, but a larger number was obtained from 

 about the base of the eye than from any other part of the ten- 

 tacle, which might indicate that there is an accumulation of these 

 cells at this place. Of these the multipolar type shows the highest 

 grade of development. The usual form is that of a somewhat 

 triangular central portion, containing a large nucleus at or near 

 the middle, and out-branchings at two or all three of the corners 

 (pi. 15, fig. 14). These branches may extend for some distance 

 with no apparent divisions, or they may divide into smaller div- 

 isions until presiunably they form a fine network of interlacing 

 fibers ; though if such be the case they were broken in the prepara- 

 tion so that only the trunks of such branches were left. Plate 15, 

 figure 12, shows four such cells with their processes crossing a 

 number of muscle fibers. That these multipolar cells occupy a 

 definite place in the eye is shown in plate 14, figure 4. The two 

 upper branches from it ramify through the spaces between the 

 cells, but no direct connection between the fibrillae of the ganglion 



