The Central Nervous System 

 of a Cumacean 



WILLIAM A. HII.TOM 



The species studied was deleimined by tlie V. S. Nat. Miis. to lie Cnliirnslylis 

 occidentalis Caiman. 



Specimens were tixeil in tiie usual reagents, Flemniing's fluid and Mercuric 

 chloride were especially used, and sections were made of the whole body. Altliough 

 the animals are small some difficulty was encountered in sectioning, but a few per- 

 iect series were obtainetl ; tliat is, perfect in most respects, for in many cases parts 

 of the specimen crumbled in cutting or fell from the slide before mounting. To 

 supplement the sections, the nervous s\stein \vas exposed with needles and remo\-etl. 

 This proved to he c|uite ditficult but a few perfect dissections were made and the 

 ganglia removed, stained and mounted. Such small bits of tissue were hard to handle 

 because easiU' lost in stains, so dilute solutions \\ere used for a long period. 



The central nervous system consists of the brain, eleven thoracic ganglia and six 

 abdominal ganglia. The three ganglia just below the brain are almost fused into one 

 mass and the other ganglia of the thoracic region are Unequal distances from each 

 other, the last three being separated from the others and quite close together. The 

 last abdominal ganglion is wider than the others but not much larger. Running 

 between the connectives a very fine median ncr\'e was found. 



The brain has quite well marked tracts connecting its parts with each other and 

 with lower levels. Figs 2 and 3. The ventral ganglia of the thoracic region have 

 the usual distribution of cells as shown in section. Figs 4 and 5. In surface view 

 the thoracic ganglia are seen to have definite cell groups. Fig. 7. The abdominal 

 ganglia are much simpler as shown in the cro*s section. Fig. 6; and the whole 

 mount. Fig. S. The last abdomiiial ganglion has more cells, Fig. 9, but there are 

 not so many isolated groups as in the thoracic ganglia. 



I ha^■e been unable to find atu' recent literature relating to the ner\'oi s s>stem 

 of ciunaceans. 



The following general jioints seem true; 



I. 'Fhe brai[i is more complicated than the si/e of ihe auinial seems to indicate, 

 more so than primitive Crustacea, such as Kranchipus, or Neballa. 



Z. The arrangement of the ganglia shov\s a considerable nuidification from a 

 simple condition. 



3. The lack of complex structures in the ahdnminal region brings about a simple 

 condition of the ganglia in this part. 



{Cinili ilnitiiiti jriiin llic '/.iiiilmjii al Drl'iirtiniiil nj I'lmnuui ('nllvijc) 



