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 trachez, as is well known, are composed of two coats : 
the inner coat forms the envelope of the aériferous canal; the 
outer coat, or peritracheal membrane (peritoneal membrane of 
the Germans), surrounds the former envelope, leaving an in- 
terval, the peritracheal space. But at the point where the 
trachex penetrate between the muscular fibres, the inner coat 
disappears, and the aériferous canal terminates ceecally, 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 aériferous 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 lacunze; the lacunar currents convey it again to the 
dorsal vessel. 
Thus, to sum up, the trachez of insects, which are aériferous 
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, Oliv.). 
By T. THORELL*. 
Tuis large and well-marked Epeirid, which Pallas described 
and figured in 1772 (in ‘Spicilegia Zoologica,’ t. i. fase. 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. 
