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. [Illustration: _Plate XIX._] It will be seen by a reference to Plate XIX.,[144] figs. A and A 1, that in addition to the cylindrical branch, which mounts upwards, there is a shorter branch which leaves the main tube on the opposite side (on the left as seen in the Plate), and takes a downward course. Now this descending branch, which is barely more than an inch in length, is a cavity of variable form, being sometimes cylindrical, and sometimes egg- or even watch-shaped,[145] but there is one particular in which it never varies, and that is the position of its elliptic orifice. This orifice is always situated on the opposite side of the main tube to that on which the ascending branch leaves this latter, so that the whole nest, when seen in section, presents the figure of a St. Andrew's cross, only with arms of unequal length. [Footnote 144: A nest of a scarcely half-grown spider is here represented in order that sufficient space might be gained to show the lower door in its two positions. The perfect cavity is still found in nests of much larger dimensions, and occasionally, indeed, in nests of almost the maximum size.] [Footnote 145: I take the liberty of coining a word to replace "lenticular," the form of a watch being more familiar than that of a lens.]