This is borne out by the fact that such a door will, on examination, be found to consist of several layers of silk, with more or less earth between each, these layers decreasing in size from without inwards, and together forming a sort of saucer in which the small central mass of earth lies. Thus by moistening a series of the cork doors of _Nemesia cæmentaria_, I have been able to detach, in one of medium size, from six to fourteen circular patches of silk, of which the outermost, or that which forms the lower surface of the door, is the largest, and the innermost the smallest, the others being intermediate in size as in position. Perhaps if I had had larger doors at my disposal for examination I might have found more layers, as other authors[84] speak of a much greater number of layers in the cork doors of _Cteniza fodiens_. Be this as it may, I am confirmed in my opinion that the layers of silk mark the successive enlargements of the nest by the additional fact that in very small doors the layers of silk are few or single, and that a proportion is observable as a rule between the size of the door and the number of layers of which it is composed.[85] [Footnote 84: M. de Walckenaer seems to have found more than thirty alternate layers of silk and earth in one of the doors of _Cteniza fodiens_, as we may gather from the following:--"Quoique cette porte n'ait guère que trois lignes d'epaisseur, elle est formée par la superposition de plus de trente couches de terre séparées les unes des autres par autant de couches de toile. Toutes ces assises successives s'emboitent les unes dans les autres comme les poids de cuivre à l'usage de nos petites balances. Les couches de toile se terminent au pourtour de la porte." Walckenaer, Histoire des Insectes Aptères (Suites à Buffon), vol. i. p. 238 (Paris, 1837). I have not found the regular layers of earth and silk of which M. de Walckenaer speaks, the silk layers being usually in contact at their centres and only separated by a little ring of earth interposed between their edges, this earth being thickest towards the circumference of the layers of silk.] [Footnote 85: This may be seen by the comparison of the composition of doors of different sizes, given in Appendix H.] Another proof that enlargement takes place, may at times be found in the nests of _N. Eleanora_, where one, or even two useless doors may be detected behind the lower door.