170 ALEXANDER PETRUNKEVITCH 



Nine single interneiiral vertical arteries connect the supra- 

 neural with the subneural artery. These vertical arteries pass 

 exactly between adjoining neuromeres, the first artery separa- 

 ting the pedipalpal from the first pedal neuromere, the ninth 

 lying immediately behind the fourth abdominal neuromere of 

 the suboesophageal ganglionic mass. Median longitudinal con- 

 necting vessels seem to exist between all vertical arteries, but 

 only between the fifth and sixth, and between the sixth and 

 seventh vertical arteries the connecting vessels are invariably 

 well discernible, as shown in figure 1. 



The subneural artery does not extend beyond the suboeso- 

 phageal ganglionic mass, but ends behind the fourth abdominal 

 neuromere, where it receives the ninth vertical artery, which 

 may be, therefore, in a way regarded as a direct continuation of 

 the subneural artery. At the place of their junction a single 

 blood vessel is given off ventrallj^ This is the comb-artery 

 sho^kTi in figures 1 and 5. It gives off a pair of branches, one for 

 each comb, and another pair of smaller branches for the genital 

 opercula. 



Each cephahc artery gives off several branches, the most 

 important of which is the ophthalmic artery shown in figure 1. 

 Beyond the ophthalmic artery the main vessel may be termed 

 cheliceral artery. Inside the chelicera the cheliceral artery forms 

 two ramified branches, one for the flexor and the other for the 

 extensor of the movable finger. 



COMPARISON WITH SPIDERS 



Having thus described the most important features of the cir- 

 culatory system in scorpions, we now. may proceed to its com- 

 parison with the corresponding system in spiders. A glance 

 at plate 3 of my paper pubhshed in the Zoologische Jahrbiicher 

 for 1920, vol. 31, will reveal both the similarities and diversities 

 of structure. What I described there as 'Kopfarterie' corre- 

 sponds with the cephahc artery of the scorpion almost to the 

 minutest details, and shows the same ramifications. On the other 

 hand, in the spider the cephalic arteries represent the upper 

 branches of the thoracic arteries, the lower branches of which 



