248 Miscellaneous. 



Note on the Arterial St/stem of the Scoiyions. Hy M. F. Hotjssay. 



The arterial sj-stem of the Scorpions is formed by two groups of 

 vessels, one dorsal, the other ventral, united on the one hand by 

 two short vessels at the anterior part and on the other by an un- 

 paired duct situated in the median part of the animal's body. 



Dorsal group. — From the heart, which is entirely seated in the 

 preabdomen, two aortas start anteriorly and posteriorly. The 

 anterior aorta passes without ramification to the cerebroid ganglia, 

 where it suddenly terminates. From the termination issue four 

 arteries — two which pass to the dorsal eyes of the cephalothorax, 

 and two others which run to the chelicera, furnishing in their 

 course a branch for the lateral eyes and another which is distributed 

 to the muscles. The posterior aorta traverses the post-abdomen, 

 and ramifies in a very homogeneous manner in all the segments. 

 At the anterior part of each segment it gives off two very short 

 arterioles, and in the middle of the segment two stouter arteries 

 which bifurcate into two branches perpendicular to their direction. 



Ventral group. — This is the most interesting from the relation 

 which it presents to the nervous system. It consists of a lacuna 

 which surrounds the oval ganglionic mass of the cephalothorax and 

 of a vessel enclosed in the sheath of the abdominal nervous chain. 

 The blood occupies the space enclosed between the two nerve-fila- 

 ments, which run from one ganglion to another, and spreads around 

 each ganglion in such a way as to form at this point a small lacuna. 



From the cephalothoracic perinervous lacuna issue on each side 

 five trunks, which run to the legs. The blood and the nerve of 

 each leg are at starting in the same envelope. 



All the ramifications starting from the abdominal canal issue at 

 the level of the ganglion, and there also a nerve and a blood-current 

 quit the common envelope together. 



Communicating arteries. — These two groups are united at the 

 anterior part by two vessels, which embrace the digestive tube. 

 These two vessels envelop the commissures which run from the 

 cerebroid ganglia to the ventral mass. They place the perinervous 

 lacuna in communication with the termination of the anterior aorta. 

 The blood is not diffused around the brain, whether it be that these 

 ganglia have a special envelope, just permitting the issue of the 

 commissural nerve-filament in order that it may penetrate into the 

 blood-vessels, or that the common envelope is so closely applied to 

 the nervous mass that the blood cannot penetrate between them. 



The other communication between the two groups is established 

 by a vessel which starts from the posterior aorta at the middle of 

 the seventh segment of the preabdomen. It buries itself between 

 the two small lobes by which the liver is produced into the post- 

 abdomen ; then it passes to the right of the digestive tube and opens 

 into the perinervous lacuna at the level of the ganglion of the first 

 segment of the postabdomeu. 



This relative arrangement of the circulatory and nei^vous systems, 

 already indicated in Limulus and the Myriopoda, is thus found to 

 extend also to a group of Arachnida. — Com pies llendvs, August 2, 

 1880. p. 354. 



