THE DIENCEPHALON. 59 



The middle portion of the cheliceral neuromere forms the posterior portion of 

 the great mass of commissural fibers and neuropile upon which the hemispheres 

 rest. (Fig. 48, b and c.) One may recognize in it: coarse fibers of the lateral cell 

 clusters, Co^; fibers from the large, central cells of the olfactory lobes (Figs. 

 48 and $i,ol.c\); a dark, central mass of neuropile, b. in which innumerable neu- 

 rites, apparently from all parts of the brain, terminate; and a thin layer of com- 

 missural fibers extending from one crus to the other, c. 



The more anterior portion of the commissural mass (Fig. 48), represents the 



..s.c.riD. 

 k G.ctf 



Fig. 49. — Diagonal section of the forebrain of a young Limulus (about four inches long) , methylene-blue prepara- 

 tion stained with carmine. Camera outlines. 



commissural bundles of the second and third forebrain neuromeres, a and d; 

 and the several olfactory, ol.c^"*, and optic commissures, op.g.'*^ . 



The Stomodaeal Ganglia and The Suprastomodaeal Commissure. — The 



cheliceral neuromere is always intimately associated with the system of stomodaeal 

 nerves and ganglia. The lateral stomodaeal ganglia lie on the median side of the 

 nerve cords, st. g. The stomodaeal commissure, st.c, which always crosses in front 

 of, or over, the stomodaeum, forms one of the most conspicuous and constant 

 landmarks of the arthropod brain. 



In the scorpion, the anlage to the lateral stomodaeal ganglion may be faintly 

 seen from the surface, on the anterior median face of each half of the cheliceral 

 neuromere. (Figs. 14 and 15, st.g.) The same anlage may be seen in sections, 

 in Blatta, Acilius, Buthus and Limulus, as a thickening or evagination of the side 



