Before proceeding to pass briefly in review what has been written on the subject of trap-door spiders, it will be well to take one glance at the relation which these spiders bear to their fellows. The great order of spiders (_Araneæ_) has recently[47] been divided into seven sub-orders, the fourth of which, _Territelariæ_, includes all the trap-door spiders, and some others which do not construct trap-doors. This sub-order corresponds with that which was formerly called _Mygalidæ_, but this name, as well as that of _Mygale_, originally given to all trap-door spiders, has been abandoned because this latter name had previously been applied to a genus of Mammals, and it was feared that confusion might arise. [Footnote 47: Thorell, On European Spiders, in Nova Acta Reg. Soc. Scient. Upsaliensis, ser. iii. vol. vii. fasc. 1 and 2 (1869-70).] The _Territelariæ_ [or underground weavers] are distinguished from all other spiders by the position of their falces,[48] which have the fang directed downwards, and move vertically parallel to one another. Thus when a victim is seized by one of the _Territelariæ_ it receives a downward blow, while other spiders strike sideways, the falces moving in a horizontal or oblique direction. With very few exceptions this sub-order may also be known by the presence of four blotches of paler colour at the base of the abdomen underneath, indicating the position of four air-sacs, almost all, or indeed perhaps all, other spiders having but two. [Footnote 48: Sometimes called mandibles. One of these is represented, enlarged, at Fig. A 7. in Plate VII., p. 88.] Certain species of _Territelariæ_ are the only spiders known to construct nests closed with a door, and these creatures must be admitted to rank among the first of Nature's handicraftsmen and inventors. The geometrical webs of many common spiders are very beautiful structures, but these are for the most part only snares for prey, and not permanent dwellings, although the cocoons in which the eggs are placed are often most ingeniously contrived. Thus in the south we may sometimes find an inverted balloon of strong silk about an inch long attached to heath and other bushes, which, if examined during the winter, will be found to contain in its centre a case enclosing a mass of eggs about one-third the bulk of the entire cocoon. This inner case is shaped exactly like the outer, and both have a circular silk lid carefully closed, and the space between the two is filled with a dense mass of golden-brown silk, which acts no doubt as an excellent non-conductor. This cocoon is the work of _Epeira fasciata_, a species apparently only found in southern Europe.