THE CENTRAL NERVOUS SYSTEM OF THE PARASITIC 

 ISOPOD, GRAPSICEPHON 



William A. Hilton 

 Department of Zoology, Pomona College, Claremont, Calif. 



Some specimens of the genus Grapsicephon of the Bopyridae were 

 obtained from the gill chambers of the common shore crab of Laguna 

 Beach, Pachygrapsus crassipcs Rand. One of these was sent to the 

 United States National Museum and there determined to be of the 

 genus here given. 



Two' specimens were sectioned and mounted in series ; one was 

 stained in carmine and one in hematoxylin. Only in the latter speci- 

 men was the poorly developed nervous system distinguished easily 

 from the surrounding tissues. No supraesophageal ganglion was found 

 and the ventral chain of ganglia was imperfectly developed. The 

 whole central nervous system does not exceed one millimeter in length, 

 or a little less than one twelfth the length of the animal. A wax recon- 

 struction was made of the central nervous system showing the loca- 

 tions of the cellular areas. 



There are at least four ganglia represented in the nervous system, 

 but these are very imperfect and irregular ganglia. Beginning at the 

 cephalic end the ganglion is quite well fused and occupies one third 

 the whole length with no branches for some distance ; then there are 

 large irregular branches extending laterad. Next there is a division 

 into something like connectives and other branches extending laterad, 

 although these do not show well in the model, because they seem fused 

 with the other parts. Near the caudal end of the ganglionic mass 

 there are other divisions into connectives and near these, short 

 branches. Altogether, there are six very irregular pairs of lateral 

 branches which could be followed only for a short distance from the 

 central nervous system, and four branches which arise from the caudal 

 end. 



The distribution of cells is on the whole much like that of other 

 arthropods. Most of the cells are ventral in position, but irregular 

 masses are seen at places on the dorsal side. The cells in many cases 

 seem but poorly developed ; the nuclei in some cases are like those of 

 nerve cells, but most of them appear like poorly preserved material, 

 although the general preservation of all parts of the specimen except 

 this was very good. 



In conclusion, it might be said that the animal has a degenerated 

 central nervous system with indications of at least four ventral fused 



