THE CELL CLUSTERS OF THE BRANCHIAL NEUROMERES. 



75 



outward into the haemal nerve. It there divides into two bundles; one l.ah, con- 

 stitutes the nerve supplying the haemo-neural and longitudinal abdominal muscles; 

 the other, extending onward into the main trunk, forms the branch that supplies 

 the branchio-thoracic muscles (hypoglossal elements). 



e. A group of large cells, lying on the posterior haemal side of the pedal 

 ganglion. (Figs. 60, 61, 63, and 64, E and e.) Their axones are directed diago- 



FlG. 62. — Anterior branchial neuromere of a young Limulus seen from the heemal surface. On the right, the 

 superficial, longitudinal, hsemal tracts are shown; on the left, the underlying haemal cross commissures, and their 

 relation to the principal groups of neurones. Outside the main figure, on the left, is a cross-section of a neural 

 nerve, N. N', and a haemal nerve, H. N, On the right, the minute structure of some of the nerve tubes in 

 the haemal nerve, m. t, and in the neural nerve, -r. t, is shown. 



nally forward, inward and upward; they then cross over to the opposite side, and 

 return again to the haemal surface where they extend forward as fine unbranched 

 fibers on the lateral margins of the longitudinal, haemal tracts. 



The crossing bundles constitute apparently the whole of the posterior neural 

 commissure. (Fig. 64, p.n.co.). Before and after crossing, the axones give ofE 

 numerous dentrites which ramify in the neuropile core of the pedal ganglia (Fig. 

 63, E.) Probably association fibers. 



/. A medium sized cluster on the anterior lateral margin of the pedal ganglion. 



