Pomona College, Claremontj California M 



folding oi the nerve cord within the muscle bands; the nerve tissue 

 docs not seem to be clastic. 



Very little has been written on the histological structure ot 

 sipunculids. Haller, 1SS ( ), discusses a number ot points, especially 

 in sipunculus nudus, relating to the ventral cord only. I find a num- 

 ber of differences in this form. 1 did not find any very clear evidence 

 of special neuroglia cells, such as described and figured by Haller, 

 such elements may be present, but at least they are not evident, 

 not so evident as in many other invertebrates which 1 have exam- 

 ined. Nerve cells may anastomose with each other as shown in 

 1 [aller's figure, but o\ this I can not be sure. If fibres olo not unite 

 they arc in very intimate contact. 



In the ventral cord wo small fibrils were seen only rather small 

 libers which may have been fibrils. The lack of connective material 

 in part at least, perhaps because the nervous system is often extended 

 and folded, shows the cell processes with great distinctness. This 

 may be why a clearer picture than usual is presented ot the relation- 

 ship ot cells. 



Cells are abundant on the ventral side ot the cord, especially in 

 the middle line. The more dorsal fibrous region is practically with- 

 out cells iA any kind. No very marked tracts of fibers arc evident, 

 the fibers arc about equally distributed in all directions and may be 

 subdivided as follows : 



1. Fibers which enter the fibrous mass from cells and run short 

 distances up and down. 



2. Fibers which pass from cells to other cells near by in the 

 celular area. 



.V Fibers which leave the ganglion laterall) from ventral cells. 



4. Fibers which enter from the lateral nerves to end in the fiber 

 area or in among the cells. 



There are no indications i)\ long fibers, either ascending or 

 descending. After the examination o\ the cord ot this animal one 

 is impressed with the suggestion that main cells ot similar sort act 

 alike, that is groups oi cells, not individuals are involved in the 

 simplest transmissions o( impulses. This general suggestion which, 

 o( course, is not new, comes to mind with great clearness after the 



