in the Spiders of the Genus Lycosa. 1 9 



immediately into two branches, one of which bends forwards to 

 reach the aorta, whilst the other curves backwards so as to con- 

 tinue its course as far as the posterior extremity of the heart, 

 receiving in its passage affluents from the other apertures. It 

 is thus only the shortest portion of the heart that drives the 

 blood in the same direction as the heart of the other Arthropoda. 

 It is true that, if this portion is short, it is at the same time the 

 widest part of the dorsal vessel. 



The posterior part of the dorsal vessel is simply tubular, and 

 may bear the name of the posterior or caudal aorta. It penetrates 

 into the apex of the abdomen, which may be called the pygidium, 

 where it is found gaping widely into a lacuna which occupies 

 this pygidium and the base of the spinners. The form of this 

 orifice is oval ; under the microscope it is seen to be constantly 

 giving passage to a large stream of blood which pours into the 

 lacuna of the pygidium. 



No doubt these are not the only apertures by which the blood 

 quits the heart. I have described above the conical processes or 

 diverticula which this viscus presents at the level of each pair of 

 venous apertures. These processes are prolonged into whitish 

 bands, which turn round the sides of the body, and descend to- 

 wards the ventral region of the abdomen. I regard these bands 

 as arteries ; but I must admit that, as these organs are only of 

 small diameter, and repose upon a somewhat opake vitelline 

 mass, I have never succeeded in seeing blood-globules moving 

 in their interior. Hence I cannot arrive at complete certainty 

 upon this point. I am aware that, according to M. Pappenheim*, 

 the heart in Spiders does not present any trace of lateral vessels, 

 and gives origin to vascular trunks only at its two extremities ; 

 but I cannot attach very great importance to the assertions of 

 this anatomist, seeing that he represents the heart in Spiders as 

 enclosed in a pericardium which presents no aperture. He thus 

 appears implicitly to assume that one extremity of the heart is 

 venous and the other arterial, and seems to have had no know- 

 ledge of the lateral orifices. This notion is radically wrong; and 

 M. Pappenheim may equally well have deceived himself with 

 regard to lateral arteries. I would rather rely upon the old but 

 skilful dissections of Treviranus, who found lateral arteries in 

 the heart of Tegenaria domestica ; moreover it would be an 

 arrangement exactly conformable to that described by Newport 

 in the Scorpions. 



It is true that M. Blanchard, resuming a theory which was 

 only doubtfully put forward by Dugesf, regards these organs 



* Comptes Rendus, 1848, tome xxvii. p. 159. 



t Additions au Memoire de M. Duges sur les Araignees (Ann. Sc. Nat. 



2* 



