COMPAliATIVE MOEPHOLOGY OF THE GALEODID^. 313 



limbs tliey innervate, which, as we have explained, was probable the original specialization of the Arachnids 

 as a class. The Spiders show but little advance on this. The Galeodidae, in spite of the comparative 

 freedom of the three posterior segments, show greater concentration of the ventral segmental ganglia 

 than do the Aranese with their moi-e uniform fusion of the cephalothoracic segments. Scorpio shows 

 still greater specialization, the ganglia are pushed forward so as to form an almost cubical mass sur- 

 rounding the (Esophagus. Lastly, iu Phalangiuin, the forward movement of the limbs and genital 

 aperture has thrust the segmental ganglia of the cephaiothorax forward and upward till they lie almost 

 in the transverse plane. 



Pt'iiicipcd Nerves. — Thenervos leaving the central nerve-mass of Galeodes are : — 



(1) The optic nerves, which run forward from behind, I'emaining in contact with the 

 hrain before bending upward to the eyes (PL XXXI. figs. 2, 5, on). 



(2) The cheliceral nerves (figs. 4, 5, ch), which rise just in front of the optic nerves, 

 and soon give off a branch [ch!) to the cheliceral muscles. 



(3) The powerful nerves to the pedipalps, wliich are double, dividing into smaller 

 dorsal and larger ventral branches soon after leaving the brain (fig. 6, pp). 



(4, 5, 6, 7) The nerves to the other limbs, all of which are double, a fact which was 

 recognized by Kittaiy, but only noticed for the two posterior legs by Blanchard. Iu 

 each of the last two limbs the smaller branch accompanies the mid-gut diverticulum. 



(8, 9) Three long nerves, which run straight backward from the posterior ventral end 

 of the nerve-mass, one in the median line and the other two on each side of it. They 

 run through the neural aperture of the diaphragm (i)). The lateral nerves {g) supply the 

 genital glands : while the median {ah) is the main abdominal nerve, which, after passing 

 through the neural arch of the diajihragm, swells into a large ganglion, the abdominal 

 ganglion ; it then runs backward immediately under the central canal of the mid-gut, 

 innervating it and the stercoral pocket, and also apparently sending up nerves among the 

 digestive tubules. 



(10) Nerves which appear to leave the posterior end of the dorsal (supra-oesophageal) 

 portion of the mass to supply the mid-gut. So far as I can make out, these do not leave 

 the brain in compact bundles of fibres, but spring from the whole posterior surface of 

 the brain wherever the alimentary canal is in contact with it. I have assumed that the 

 centre is the mass which lies behind the optic ganglia, but I failed to find any very 

 clear connections. 



(11) The paired (or unpaired) nerves which leave the brain between the cheliceral 

 nerves and supply the labruni (PI. XXXI. fig. 6, L). 



(12) Paired nerves leaving the anterior end of the ventral portion of the nerve-mass, 

 supplying the labium. 



(13) Two small nerves leave the brain on each side between those running into the 

 2nd and 3rd legs (or else branch from these in some way), and run to the stigmatic 

 apertures (fig. 6, stig.). 



Peripheral Nerves. — Of the peripheral nervous system I have been able to fi.nd only 

 traces. A network of fibres runs in close contact with the hypodermis, supplying the 

 cuticle and hairs. These nerves are sometimes marked out in white in parts of the dorsal 

 sm-face where pigment has collected. I have not succeeded in tracing these integumental 

 nerves to their sources. 



