TRAP-DOOR SPIDERS. 125 



forms the lower surface of the door, is the largest, and 

 the innermost the smallest, the others being inter- 

 mediate 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* speak of a 

 much greater number of la3^ers 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 suc- 

 cessive 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, t 



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. 



Now when there are three lower doors in this way 

 the one which is in use is the largest, and the door lying 

 nearest to this one the next in size, while the hindmost 

 is the smallest of all. But though those abandoned 

 doors are now too small to fit the existing tube, they 



* M. de Walckenaer seems to have found more than thirty alternate layers 

 of silk and earth in cue of the doors of Cteniza fodiens, as we may gather 

 from the following : — " Quoique cette porte n'ait guere que trois lignes 

 d'epaisseur, elle est form^e par la superposition de plus de trente couches de 

 terre s^parees 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 cuiv^re a I'usage de nos petites balances. Les couches de toile se termi- 

 nent au pourtour de la porte." Walckenaer, Histoire des Insectes Aptferes 

 (Suites k Buffon), vol. i. p. 238 (Paris, 1837). 



I have not found the regular layers of earth and silk of which M. de 

 Walckeuaer speaks, the silk laj-ers 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. 



+ This may be seen by the comparison of the composition of doors of 

 different sizes, given in Appendix H. 



