This new type is strictly intermediate between the double-door unbranched wafer nest constructed by N. Eleanora, and the double-door branched wafer with the descending cavity which I am now about to describe.
This latter nest, the work of N. Manderstjernæ, Auss.[143] (formerly called N. meridionalis), has already been partially made known by the figures and description given of it in Ants and Spiders (Plates IX., X., and XI., pp. 98, 100, and 104); but I have to confess, with great regret, that when these illustrations and descriptions were published, I was not fully acquainted with the true structure of this nest, having overlooked the existence of a short descending cavity which leaves the main tube a little above and on the opposite side to the ascending branch. This cavity is always present, but the very largest and oldest spiders usually allow it to become filled up with remains of food and particles of earth, and sometimes even spin silk across its entrance, in which case it can only be traced on very close examination.
[143] This spider was described by Mr. Pickard-Cambridge at p. 101 in Ants and Spiders, under the name of N. meridionalis, Costa. This name has now to be abandoned for reasons given in full by Mr. Cambridge at p. 283, below. It would appear that a spider discovered by M. Simon in Corsica corresponds more closely with the N. meridionalis of Costa than our spider of the Riviera does. Moreover, since Ants and Spiders was written I have had the good fortune to obtain at Mentone four male examples of our supposed meridionalis, and these prove to possess the same characters as those assigned by Prof. Ausserer to a male spider which was captured at Nice, and named by him N. Manderstjernæ. This specimen is now in the possession of Dr. L. Koch, to whom I am much indebted for having kindly entrusted it to me for examination. This enabled Mr. Pickard-Cambridge to assure himself of the specific identity of his N. meridionalis with N. Manderstjernæ, which latter name it must for the future bear.
It was from an old nest such as this, in which the descending cavity had been closed up, that the large drawing at fig. A on Plate IX of Ants and Spiders was made, and this figure, therefore, still remains substantially correct.
But in the case of the other illustrations—namely, fig. B, Plate IX, fig. A, Plate X, and figs. B and B 1, Plate XI, where nests of young spiders, or of spiders which, though adult, have not attained the maximum size, are represented, this descending cavity, though overlooked by me, should have been shown, for it must certainly have existed.
Its presence was first observed by the Honourable L. G. Dillon, who detected it when tracing the course of the main tube upwards from below. I had always followed the tube from above downwards, and in so doing must have unwittingly filled up the descending cavity (the existence of which I was far from suspecting) with detached particles of earth.
I will own that, when Mr. Dillon first showed me this new feature, I hoped that it might prove to be something accidental and exceptional; and it was only after careful examination of a large series of nests of all sizes, that I gradually and almost unwillingly admitted that this descending cavity formed an important feature in the typical structure of the nests.
I now see, however, that the presence of this cavity adds considerably to the interest of the structure as a whole, and places its architect quite at the head of all the builders of trap-door nests. This type should now be called, for the sake of distinction, the double-door, branched, cavity, wafer nest, to avoid confusion with the Hyères branched nest.
I am now about to endeavour to atone for my past oversight by giving new illustrations ([Plate XIX], figs. A and B) and descriptions of this very remarkable nest; while I would at the same time beg the indulgence of my readers for past and present shortcomings, reminding them that the interest which attaches to structures of this kind is proportioned to the complexity and subtlety of their contrivance, and, therefore, to the difficulty we experience in properly understanding and describing them.
Plate XIX.