I have represented at B 1 the 14 layers of silk and earth which went to make a single cork door examined by me. It will be seen that the outermost of these layers is the largest, and the innermost the smallest, and I have already (_Ants and Spiders_, p. 150) shown reason for believing that the latter constituted the first door the spider ever made, and that the consecutive layers mark successive stages in the enlargement of the nest. There is therefore a broad distinction as to construction between cork nests and wafer nests; moreover, while the former are, as far as we know at present, all of one type, and only differ in size or proportion, the latter appear under five distinct types. Thus, every known cork nest, whether found in Europe, America, or the Antipodes, has the same solid door and simple tube; while of the wafer nests, some have branched and others simple tubes, and some again possess a lower door in addition to the upper or surface door. In the following pages I intend to treat of the trap-door spiders and their nests in the same order in which the latter are placed in the diagram, commencing with those of the cork type B, and then dealing successively with the several wafer nests from C to G. We have already spoken of A, the nest of _Atypus piceus_, and seen that our present knowledge of this nest, of the habits of its occupant and of those of its relations, is still far from complete. The cork type is, as my readers will perhaps remember, the great cosmopolitan type which ranges round the world, and which, curious to say, is built by many different spiders belonging to distinct genera. The idea of planning this very perfect bit of mechanism appears to be the common inheritance of these several spiders, separated though they are by wide intervals of geographical space as well as to structural divergence. At Mentone two distinct spiders construct nests of the cork type, one of these being a _Nemesia_ and the other a _Cteniza_. They are as unlike each other as they well can be, and it seems remarkably strange that their nest-building instinct should be so similar. The nest of the _Cteniza_ is indeed shallower than that of the _Nemesia_, and a practised eye can usually trace a difference between the slightly less angular lower surface and more semi-circular outline of the door of the former, and the more abruptly bevelled and more circular door of the latter. These spiders and their nests have been already described and figured in _Ants and Spiders_ under the names of _Ct. fodiens_ and _Nemesia cæmentaria_. Recent discoveries have however shown that these spiders possess distinctive characters of their own, and, though closely allied to the species indicated, should be separated from them.