186 M. T. Thorell on Aranea lobata. 



have been singularly aided by the very perfect immersion- 

 objectives which M. Nachet was kind enough to place at my 

 disposal. 



It is necessary to give a precise explanation of the structure 

 of the arterioles and their mode of distribution. 



The tracheae, as is well known, are composed of two coats : 

 the inner coat forms the envelope of the aeriferous canal ; the 

 outer coat, or peritracheal membrane {peritoneal membrane of 

 the Grermans), surrounds the former envelope, leaving an in- 

 terval, the peritracheal space. But at the point where the 

 tracheae penetrate between the muscular fibres, the inner coat 

 disappears, and the aeriferous canal terminates caecally, whilst 

 the outer coat or peritracheal membrane becomes the wall of 

 the blood-vessels or arterial capillaries. It is not only the 

 spiroid thickening of the inner coat, or spiral filament, that 

 disappears, it is the inner coat itself that stops and suddenly 

 closes the aeriferous canal. In this way we see, starting from 

 a more or less voluminous tracheal stem, very delicate blood- 

 vessels, in larger or smaller number, which divide and sub- 

 divide regularly to their extremities. 



The blood retained in the peritracheal space remains through- 

 out its course in contact with oxygen ; it reaches the capillaries 

 perfectly vivified, and is a true arterial blood. The capillaries 

 are not in communication with venous capillaries ; the blood 

 diffuses itself through the tissues, nourishes them, and falls 

 into the lacunae ; the lacunar currents convey it again to the 

 dorsal vessel. 



Thus, to sum up, the tracheae of insects, which are aeriferous 

 tubes in their central portion and blood-vessels in their peri- 

 pheral part, become at their extremities true arterial capillaries. 



XVIII. — On Aranea lobata, Pallas (A. sericea, OUv.). 

 By T. Thorell*. 



This large and well-marked Epeirid, which Pallas described 

 and figured in 1772 (in ^ Spicilegia Zoologica,' t. i. fasc. 8. 

 p. 46, tab. 3. figs. 14, 15) under the name of Aranea lobata^ 

 and of which arachnologists have hitherto possessed only 

 doubtful or incorrect notions, is, as the following remarks will 

 render evident, identical with the form known under the ap- 

 pellation Argiope 1. Epeira sericea (Oliv.), which, by its size 

 and beauty, its unusual aspect, and its general occurrence, 

 attracts notice more than any other species of spider, except 



* Translated from the ' Ofversigt af Kongl. Vetenskaps Akademiens 

 Forhandlingar/ 1867, No. 9^ by Arthur W. E. O'Shaughnessy. 



