22 ON A NEW SPECIES OF ENTEROPNEUSTA, 



Nerve Cord of Collar : The collar nerve cord (figs. 16, 17, 18, 

 C7ZC.) varies in shape in transverse sections in different individuals 

 and in different parts of the same individual, from band -shaped to 

 almost circular. In its general features the cord of this species 

 agrees with that of Ft. minuta as described by Spengel. An 

 axial canal is not present in the cellular part -of the cord, and 

 the "cord hollows" are not so numerous as in that species. Two 

 lateral longitudinal rows of "cord hollows" exist, while smaller, 

 less regularly arranged hollows may be present in the central 

 region. The entire number of hollows appearing in one section 

 is seldom greater than four. These "cord hollows" are related to 

 each other exactly as in Pt. minvta. 



I have never observed an anterior insinking of the epidermis 

 into the cellular part of the cord to form an anterior epidermal 

 pocket, but a very short and narrow epidermal pocket may exist 

 at the posterior end of the cord. 



As in all other known species of the genus, the fibrous laj^er of 

 the cord completely surrounds the cellular portion. 



With regard to the histology of the cellular part of the cord, I 

 have never been able to observe in any of my preparations the 

 giant ganglion cells described and figured by Spengel. I can 

 clearly distinguish, however, large granular nuclei, rounded or 

 oval in form, and with distinct nucleoli, which belong probably tc^ 

 what Spengel regards as the proper nerve cells. They occur 

 especially above the ventral portion of the nerve fil)re layer and 

 also in the middle region of the cord and below the thin dorsal 

 portion of the fibre layer. Round these nuclei there may some- 

 times be seen an ill-defined little staining cell body, apparently 

 branching. 



The "stalked cells," with their elongated, deeply staining, 

 narrow nuclei can also be readily distinguished. They radiate 

 outwards from the thin cuticular lining of the "cord hollows," 

 and their fibre-like ends penetrate the nerve fibre layer. Also 

 there occur throughout the cellular part of the cord, but especially 

 above the ventral portion of the nerve fibre layer, numerous 

 deeply staining rounded nuclei, with ill-defined cell l^odies. 



