THE CEPHALIC NEUROMERES. 05 



A small, posterior fasciculus, coming from the chilaria, joins the main gusta- 

 tory tract. (Fig. 65, chela.n.) 



In methylene blue, the gustatory tracts have a very characteristic appearance, 

 as each fascicle contains a great many parallel bundles of extremely minute fibers 

 that look like rows of dots. 



In sections (von Rath's method), they may be recognized by their dense black 

 masses of fine parallel fibers (except in the nodes, virhere they are twisted and inter- 

 woven) and by the small quantity of neuroglia contained in them. (Fig. 56, 



In the scorpion, a similar tract may be recognized. (Fig. 69.) But here the 

 most conspicuous portion is the immense neuropile bodies on the roots of the first 

 three vagus nerves. These nerves supply the genital papillae and the pectines, 

 and the immense size of these vagal lobes is due to the great development of 

 sensory (tactile) organs in the pectines. 



Similar lobes are seen in Limulus, but lying farther forward, and associated 

 with the immense, flabellar nerve (gustatory) belonging to the sixth pair of legs. 



III. Longitudinal Tracts. 



There are several well defined longitudinal tracts in Limulus that may be 

 traced the entire length of the brain and cord, but their relations to the various 

 centers and to the motor and sensory terminals is exceedingly difficult to deter- 

 mine. In the main, the sensory elements run on the neural surface of the cords, 

 and the motor ones on the hsemal surface. 



We may distinguish the following tracts: 



The Longitudinal Haemal Tracts of the Brain and Cord. — The haemal 

 tracts are great sheets of longitudinal fibers covering the haemal surface of the brain 

 and cord. They can be seen in von Rath's preparations, along the haemal surface 

 of the neuromeres, haemal to the transverse commissures (Figs. 55, 56, 67, 68, l.h. 

 tr). They leave the anterior and the posterior ends of the neuromere in the nearly 

 isolated haemal sections of the longitudinal connectives (Fig. 64). Midway 

 between the ganglia they cannot be distinguished from the other fibers of the cord. 



In methylene blue preparations, these fibers of the cord may be followed at least 

 from one ganglion through the next without branching, and in some cases through 

 several ganglia. In the brain, individual fibers may^ be followed the whole length 

 of the crus. (Fig. 66.) 



In the brain many of these fibers terminate in small clusters of dendrites, 

 scattered over the crura, just below the haemal surface (Fig. 66, left side) ; in the 

 branchial neuromeres they are seen on the haemo-lateral surface just neurad of the 

 longitudinal fibers. (Fig. 62, right side.) 



The fibers of the haemal tracts are derived from several sources. One impor- 

 tant source is the large cluster of B neurones on the neural surface of each bran- 

 chial neuromere. Their fibers, after reaching the haemal surface, divide, one cross- 



