42 IDA H. HYDE. 



dermal layer ; and a ganglionic and fibrous network beneath the 

 epithelial layer of the subumbrella, which I believe sent nerve 

 fibers beyond the endodermal flat epithelial-like cells, up to the 

 gelatinous layer. The manubrium contains a ganglionic and 

 fibrous network connected with large ganglia that lie along the 

 radial area and smaller ones around its margin that send fibers to 

 small sensory cells at its periphery, (Fig. 3). 



A view from the exumbrella side of the margin of the animal 

 discloses a narrow hyaline-like area between the marginal nerve 

 rings (Fig. I, /). It is along this line that the velum is attached. 

 The upper nerve ring lies therefore above, the lower below the at- 

 tachment of the velum. They are, however, not entirely dis- 

 tinct but are connected by communicating fibers that show most 

 clearly, with proper focusing, from the subumbrella side (Fig. 

 i , e}. The nerve rings are composed first of several rows of 

 closely packed bi- and multipolar cells that lie tranversely to the 

 nerve rings beneath the epithelial layer of the subumbrella 

 (Fig. i, a). They are very characteristic elongated cells with 

 large nuclei. They usually taper at one end, more than at the 

 other, and give off one or more fibers from the ends. Some of 

 the fibers extend into the velum, some bend and run at a deeper 

 level along with other nerve fibers around the margin, forming a 

 double fibrous ring (Fig. I, c}. Some fibers extend into the 

 other nerve ring, while still others extend toward the apex of the 

 bell communicating either with the nervous network of the sub- 

 umbrella, the radial nerves, or ending in muscle fibers. In ad- 

 dition to these snugly-packed spindle or ovoid-shapecl cells, 

 there are bipolar or multipolar cells, that lie at a deeper level in 

 the fibrous portion of the ring canal (Fig. i, l>}. The fibers 

 emerge from the same side of the bulging or ovoicl cells and ex- 

 tend in opposite directions among the fibers of the nerve ring 

 (Fig. i, /;). At close intervals and proximal to the transversely 

 situated cells of the lower marginal ring are, moreover, large 

 multipolar cells that send fibers toward the periphery of the mar- 

 gin as well as into the nerve ring. A row of flattened ovoid 

 bipolar cells form a third nerve ring of fibers and cells peripheral 

 to those described above (Fig. i, f). Pieces of tissue dissected 

 from the umbrella in the region of the radial canals and exam- 



