172 ALEXANDER PETRUNKEVITCH 



It is situated immediately under the oesophagus and gives rise 

 anteriorly to a thin artery which is closely applied to the inferior 

 surface of the oesophagus. This is the suboesovhageal artery. 

 The four following anastomoses are rectilinear and each gives 

 rise to a vessel which issues from the middle of their ventral 

 surface and traverses the ganghonic mass from end to end to 

 its ventral surface. Schneider gave to these arteries the name 

 of median cerebellar arteries, as he did in the case of the scorpion. 



1 prefer to call them ganglionic wediaii arteries [my vertical 

 or interneural arteries — A. P.]. The supraneural artery gives 

 also rise to a certain number of more or less short arteries of this 

 kind, the first being omitted at the beginning of the supraneural 

 artery and corresponding therefore with the sixth supraganghonic 

 anastomosis. I was able to find seven or eight such arteries, 

 thus bringing their total number to 12 or 13 . . . . What 

 Schneider does not mention is the fact that all these arteries 

 connect on the ventral surface of the ganglionic mass with a 

 median longitudinal lacune" .... (pp. 61-62). 



Although I have no conclusive evidence at this moment, 

 either to confirm or to disprove some of the statements con- 

 tained in the above quotation, it seems to me that Causard 

 has been misled by imperfect injections. We easily recognize 

 in the suboesophageal artery of Causard that portion of the 

 supraneural artery, which is shown in the scorpion in our figure 



2 as SO A. But I think that both Causard and Schneider have 

 overlooked the connection of the 'anastomoses' with the supra- 

 neural artery. Causard, indeed, has seen their connection with 

 the subneural artery by means of the vertical arteries (gan- 

 glionic median arteries). On the other hand, the number of 

 these vertical arteries given by Causard as 12 or 13 seems to be 

 decidedly too great. A careful examination of sagittal series 

 of sections through young spiders shows invariably the presence 

 of eleven distinct neuromeres in the thoracic ganglionic mass. 

 The first belongs to the pedipalpi, the second to fifth to the 

 legs ; the tenth corresponds to the same neuromere in the scorpion, 

 which in the latter is already in the abdomen. The eleventh 

 neuromere is imperfectly divided into two. The anterior portion 



