ANATOMY OF ARACHNIDS 21 



therefore, eleven post-genital segments instead of ten as in the 

 Pedipalps. 



The first abdominal segment has disappeared, although Brauer 

 ('95) found a transient rudiment corresponding to it in the em- 

 bryo scorpion. 



On examination of the suboesophageal ganglion it is found 

 that the neuromeres 1 to 5 supply appendages II to VI; the 

 seventh neuromere supplies the genital organ, the eighth neuro- 

 mere the pectens and the ninth the first lung — leaving the sixth 

 neuromere, which should supply the missing segment VII, to 

 be accounted for. This sixth neuromere is clearly mapped out 

 and is quite normal in size, but I have not been able to trace 

 nerves preceding from it. It seems probable, however, that it 

 may be used as supplementary to the pectens, for the nerve 

 supply of which there is a secondary paired nervous mass lying 

 ventrally to the suboesophageal ganglion as shown in diagram 7. 



Just ventrally to the eighth neuromere, on either side of the 

 median line, there is a large mass of nerve fibers from which a 

 cord runs posteriorly and joins the nerve from the eighth neuro- 

 mere, and another cord runs anteriorly to a point opposite the 

 sixth neuromere where there is another large swelling. I have 

 not been able to detect any direct connection between the sixth 

 neuromere and the nerve mass just ventral to it, but it seems 

 probable that there must actually be some such connection and 

 that the sixth neuromere, after the disappearance of segment 

 VII, became utilised as a secondary source of supply for the 

 pectens. 



In the Buthidae, but not in the Scorpionidae, Chactidae, or 

 Vejovidae, there is a further extension of this ventral nerve 

 mass anteriorly to about opposite the second neuromere, where 

 there is another small swelling but no direct connection with 

 the suboesophageal ganglion itself. (This extension is shown 

 in diagram 7.) 



Whatever may be the true function of the sixth neuromere, it 

 is clear that it is interpolated between the fifth and seventh 

 without having any corresponding segment to supply. Seg- 

 ment VII has disappeared, but the ganglion which originally 

 supplied it remains. 



