1902.] ANATOMY OF THE PEDIPALPI. 171 



supply the fourth, fifth, and sixth somites diverge close together 

 from a point in the third somite, whence the two strands appear 

 to be closely bound together with connective tissue. 



Since the two strands here described are formed by the union 

 of the six ner^'es svipplying the six anteiioi- somites of the 

 opisthosoma, it is not always easy to decide by dissection the exact 

 points of divergence, and it is possible that some individual or 

 specific variation will be found in this respect. In the main, 

 however, I believe the arrangement described above to be fairly 

 accurate. 



Laurie ^ correctly describes the median nerve-cord as double, but 

 was unable to ti'ace the couise and distiibution of the fine nerves he 

 noticed running alongside of it from the posterior end of the 

 prosomatic mass. Presumably, like Blanchard, he did not observe 

 that these nerves dip beneath the main cord. In connection with 

 the acid-glands he describes a convoluted mass of tubules twisting 

 about on each side of the central or right gland, and succeeded 

 in tracing two of these tubules, apparently opening into the 

 left sac. These tubules he intei-preted as the purely secretive 

 pai't of the gland. May they not have been the fine branches of 

 the inferioi- system of nerves torn from their antei'ior attachments ? 

 This view of the mattei- w^ould account for Laurie's failure to 

 trace the course and distribution of the lateral nerves passing 

 backwards into the opisthosoma from the posterior end of the 

 prosomatic ganglionic mass. 



Tarnani '^ says nothing of the nei'vous system of the opisthosoma. 

 The nervous system of the opisthosoma in Phrynas is of a far 

 more primitive type than that which I have described above in the 

 case of the Thelyphonidee. The nerves supplying the genital and 

 the two following somites have passed forwards into the prosoma 

 to join the ganglionic mass of this region, arising from it on each 

 side between the nerve for the sixth ajDpendage and the median 

 cord. The threads innervating the rest of the somites of the 

 opisthosoma spring laterally from the median cord, although well 

 in advance of the somites to which they belong. They thus 

 exhibit a marked tendency towards the state of things that has 

 been completed in the Thelyphonidse — namely, the isolation of 

 the median cord by the annexation of its latei'al threads by the 

 prosomatic mass. 



In the Thelyphonidfe it seems clear that the innervation of the 

 flexible posterior end of the opisthosoma is the sole function of 

 the median cord. If these organs were suppressed, the nerve-cord 

 would become useless and might cease to be developed. The 

 whole of the sternal surface of the opisthosoma would then receive 

 its nervous supply from the cords I have above described, which 

 would certainly be taken for the primitive median cord, although 

 they would in reality represent merely its oi-iginal laterally and 

 metamerically diverging threads. 



1 Journ. Liini. Soc, Zool. xxv. 1894. 



2 Rev. Sci. Nat. St. Petersb. 1890, no. 5, p. 255. 



