ANATOMY OF ARACHNIDS 15 



Tartarides. The arrangement of the gangha in the Tartarides 

 at first sight appears to differ fundamentally from that in the Thel- 

 yphonides, since there is, in addition to the suboesophageal, a 

 large ganglion situated in the anterior part of the abdomen in the 

 neighborhood of the genital segment instead of at the posterior 

 end of the abdomen. Microscopical examination, however, shows 

 that there are nine neuromeres in the suboesophageal ganglion and 

 eight in the abdominal ganglion, making seventeen in all — the 

 same number as in the Thelyphonides — and it may be presumed 

 that the Thelyphonides and Tartarides became differentiated 

 from a common ancestor at a stage when there were still eight 

 separate paired ganglia in the abdomen; a stage now represented 

 in the larval Thelyphonides. On further specialization the 

 ganglia in the Tartarides became concentrated into a single an- 

 terior abdominal ganglion, while in the Thelyphonides two 

 groups of three and five ganglia respectively were formed, the 

 first group passing forward to join the suboesophageal ganglion 

 and the latter remaining in the posterior part of the abdomen. 



It may be recalled that, apart from their external affinities, 

 which have led to placing these two groups in the same order, 

 the close relationship of the Thelyphonides and Tartarides is 

 clearly established by the similarity of the coxal glands — a fact 

 which makes it easier to accept this explanation of the appar- 

 ently fundamental difference in the arrangement of the ganglia. 



VI. SPIDERS 



In all spiders there appear to be twelve neuromeres in the sub- 

 oesophageal ganglion, although with the Araneae verae it is 

 not often possible to make them out except in larval and quite 

 young specimens, but the Theraphosid spiders show the neuro- 

 meres more clearly, always to the number of twelve. 



In young and adult spiders there are no abdominal ganglia, 

 nor have I ever found any trace of them in larval specimens of 

 the Araneae verae; but in 1913 I was fortunate enough to find 

 in Sumatra a cocoon of a large Chilobrachj's (Theraphosid) 

 containing nearly a hundred larvae just after hatching, and 



