THE H^MAL NERVES OF THE DIENCEPHALON AND MESENCEPHALON. 97 



codes split into a special group of gustatory organs, and into a large cranial gang- 

 lion. (Figs. 27-34.) 



The Ganglia of the Cord.Limulus. The roots of the neural nerves 

 arising from the postcephalic neuromeres are also provided with ganglia, but they 

 are not as large as those on the cranial nerves. They merge with the cord at an 

 early period, and, in the adult form the large swellings on the roots of the branchial 

 nerves. (Figs. 59-64.) 



Scorpion. In the scorpion the anterior pairs of nerves are much larger than 

 the posterior ones, and spring from the outer or neural surface of the cord. In 

 stage H, just before hatching, the root of the anterior nerve contains a large mass 

 of cells, evidently arising independently of the nerve cords, just as the pedal 

 ganglia do in the thorax. (Fig. 73, D.) In the later stages, just after hatching, 

 the ganglion is drawn toward and partly merges with the cord. In the adult, 

 ganglion cells are scattered for some distance over the root of the nerve. (Fig. 



73. C.) 



Meantime the two haemal nerves move forward, and unite to form a single 

 one with two roots, which in turn unite, a short distance from the cord, with the 

 ganglionated neural nerve. There is no actual mingling of fibers, but the nerves 

 run together, for a short distance, as a single nerve. (Fig. 72.) 



The Haemal Nerves. Limulus. A single pair of haemal nerves arise from 

 the anterior haemal surface of each thoracic nueromere. (Fig. 70, h.n.) They 

 are much smaller than the pedal nerves, without ganglia, contain motor and 

 sensory fibers and are distributed mainly to the integument and other tissues of 

 the thoracic shield. The sixth pair alone sends branches to the heart and intes- 

 tine. Near the outer margin of the entacoxite, the nerves which are elsewhere 

 round, become broad, flat bands; the parallel bundles of nerve fibers become inter- 

 woven in a complicated manner, and there is an increased number of neurilemma 

 nuclei, but no ganglion cells. Beyond this swelling, the nerve divides into two 

 main branches, n and h\ one going to the neural surface of the carapace, and the 

 other to the haemal. After several subdivisions (see original memoir) , the end 

 branches of all these nerves form a continuous, subdermal plexus, distributed 

 over the whole inner surface of the neural and haemal integument, supplying the 

 skin, glands, muscles and sensory hairs. 



Lateral Line Nerve of Cheliceral Neuromere. All these thoracic haemal 

 nerves are essentially alike, except the first one or that of the chelicerttl neuro- 

 mere. This remarkable nerve (Fig. 70, l.c.n.), at first extends forward, and then, 

 bending backward in a broad curve, extends the whole length of the body. It 

 runs close to the neural surface, just outside the bases of the appendages, and does 

 not begin to branch till it reaches a large sclerite behind the base of the sixth leg. 

 The main nerve continues beyond this point the whole length of the branchial 

 chamber, sending one small branch toward the base of each of the five gills. This 

 is a purely sensory nerve and supplies the skin lining the channel along which the 

 water is carried to the gills. It is very remarkable that this nerve should cross the 

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