^0 



not in the Crustacea most resemljling Limulus in general shape and proportions (the 

 Brachyures, e. g.), but in Arachnids and Myriopods. 



In a Scorpion [Buthus africcmus) the two cerebral or superoesophageal lobes are fused 

 together, send off nerves to the chelicera, or antennal homologues of the limbs ii iu 

 Limulus, and to the eyes ; they are connected behind with the stomatogastric nerves, 

 and laterally, by means of short and thick ' crura,' with the suboesophageal mass. This, 

 as in Limulus, represents the ganglionic centres of several pairs of nerves, including 

 those of the chelate palps, the homologues of which come off in Limulus, as in other 

 Crustacea, from the superoesophageal mass. The four pairs of cephaletral limbs suc- 

 ceeding the ' palpi ' in Scorpio, also derive their nerve-supply from the suboesophageal 

 part of the annular centre. From this are continued the ventral chords along the thorac- 

 etron, successively developing seven closely fused pairs of ganglia ; the terminal chords 

 distribute, in the pleou, or jointed tail, pairs of nerves to the right and left, and are 

 traceable to the bent and perforated tail-spine, representing a ' telson,' but forming, by a 

 mysterious modification, the poisonous weapon of the Scorpion. 



The nervous system of this ' air-breathing Merostome ' has been well figured by New- 

 port * ; and I supply additional illustrations of that of a Myriopod t, which may repre- 

 sent a condition of the nervous system m the TrUobites. 



The superoesophageal or cephalic portion of the neural axis in Julus terrestris (Plate 

 II. figs. 6, 7, 8) is more transversely extended than in Limulus, and is less obscurely 

 divided into the right and left ganglions or side-lobes, of which the u.pper and outer ends 

 are produced as short and thick optic lobes, which are resolved halfway toward the 

 compound eyes into a plexus of filaments, distributed, as in Limulus, to the component 

 ocelli. From the fore and outer part of each cephalic lobe two distinct nerves proceed 

 to the short 7-jointed antenna of its side ; below these a pair of nerves proceed to the 

 palpless mandibles (fig. 6). From the hind and underparts of the cephalic lobes the 

 thick continuations of the neural axis descend and girt the gullet, beneath which they 

 become resolved into two chords or rings : the anterior one anastomoses with its fellow, 

 forming a simple ring ; the posterior and larger chords converge at an acvite angle, to 

 be continued into the ventral body-chord, which shows little of a ganglionic structure. 

 The converging head-chords are, however, united by a transverse commissure before 

 retrograding to the ventral body-chord. This commissure and the anterior ring recall 

 the filamentary cerebral commissures in Limuhis (Plate V.) ; the anterior oesophageal or 

 pharyngeal ring in Julus is also homologous with that shown by Lyounet in the larva of 

 Cossus ligniperda. 



The stomato-gastric system begins by a single slender median chord from the hind 

 notch at the cerebral lobes, and inunediately forms, or is in connexion with, a third slender 

 ring girting the oesophagus {;ib. figs. 7 & 8), from the middle and upper part of which the 

 trunk-nerve of this system passes a short way back on the dorsal aspect of the stomach 

 before it divides. The divisions diverge at an angle of 45°, then bend, and are continued 



* Philosophical Transactions, 1843, plate xii. 



t Julus terrestris, outlined ia my ' Anatomy of Invertebrates,' p. 356, fig. 144, 8vo, 1855. 



