Pomona College, Clareinont, California 31 



folding of the ncr\c coni within the inusclf bantls; the ncrxe tissue 

 does not seem to be elastic. 



Very little has been written on the histological structure of 

 sipunculids. Haller, 1889, discusses a number of points, especially 

 in sipioiiulii.^ laiiliis, relating to the \cntral cord only- I tnul a num- 

 ber of differences in this form. I did not Hnd any very clear e\idence 

 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 ha\e exam- 

 ined. \er\e cells may anastomose with each other as shov^n in 

 Haller's figure, but of this I can not be sure. If fibres do not unite 

 they are in very intimate contact. 



In the \entral cord no 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 

 ma)' be why a clearer picture than usual is presented of the relation- 

 ship of cells. 



Cells are abundant on the \entral side of the coni, especially in 

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

 out cells of any kind. Xo \ery marked tracts of fibers are evident, 

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

 subdivided as follov^s : 



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

 ilistances up and down. 



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

 celular area. 



.^. Fibers which leave the ganglion laterally 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 of long fibers, either ascending or 

 ilescending. After the examination of the cord of this animal one 

 is impressed with the suggestion that many cells of similar sort act 

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

 simplest transmissions of impulses. This general suggestion which, 

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



