74 



MINUTE STRUCTURE OF THE BRAIN AND CORD OF ARCHNIDS. 



that constitute the exceedingly complex core of the ganglion. Probably sensory. 

 (Figs. 62, C. and 63 C.) 



d. A cluster of about thirty very large motor cells on the posterior median 

 part of the neural surface. Their axones form a compact bundle which extends 

 vertically and then crosses to the opposite side, the two crossing bundles constitut- 

 ing a large part of the posterior haemal commissure. (Figs. 60, 61, 62 and 64, 

 D and </.) 



hr 



a 



...I, r 1 



FIG. 61. One of the anterior branchial neuromeres of a young Limulus. On the right, the principal cell clusters 

 of the neural surface are shown; on the left, the principal nerve roots, fiber tracts, and neuropile centers. The 

 , capital letters indicate the cell clusters, and the small letters, the corresponding fibers; Hr. >- 6 , the five roots of the 

 hremal nerves. Composite figure, based on methylene blue and von Rath's preparations. 



The crossed fibers extend backward along the haemo-lateral side of the cord 

 to the next posterior neuromere, forming the fifth root to the haemal nerve, //. r 5 . 

 They are very conspicuous in sections on account of the large size and pro- 

 nounced coloring of the axis cylinders and their sheaths. On approaching the 

 next following neuromere, the bundle becomes more compact and gradually 

 moves toward the outer margin of the cord, where it turns sharply forward and 



