ENEMIES AND THEIR INFLUENCE. 409 



itself. The tube is composed of fragments of white silk fastened together 

 with particles of clay, etc., and so artistically disposed, one above the 

 other, that they form a scaffold, having the form of an U2)right column, 

 of which the interior is a hollow cylinder. The tube is lined with silk 

 throughout its whole length.' 



XI. 



I have no hesitation in also applying the key thus furnished by the 



habits of Tigrina to interpret the motive of Trapdoor spiders in 

 Sr)tde*s°'^ their remarkable industry. With this in mind, and aided by 



other facts and conclusions drawn from a direct study of this 

 form of nest, we may venture to approach the subject. 



M. Eugene Simon has contributed largely to our knowledge of Tunnel- 

 weaving spiders in a recent paper presented in the Annals of the Entomo- 

 logical Society of France ^ and in the Acts of the Linnean Society of 

 Bordeaux.* His descriptions are accompanied by notes upon the habits 

 and architecture of the spiders, with admirable illustrations, which greatly 

 enlarge our knowledge of the nesting habits of these interesting creatures, 

 who rank among the most skillful artificers of tlie animal world. Mr. 

 Simon's notes were made from specimens obtained in Venezuela and North 

 Africa, the Venezuelan specimens being studied personally during a visit 

 to that country. A comparative study of his papers enables us to trace 

 the progressive development of the nesting architecture of Tunnolweavers 

 from the simplest tube in the ground to the hinged doors or trapdoors 

 which close the silk lined burrows, and which are so well known for 

 their mechanical perfection. 



The simplest form of burrow is that of the Tarantulas, which represent 

 the largest known spiders. These huge arane-ads appear to depend wholly 



upon their size to resist the assaults of enemies who invade their 

 1. Taran- ^jgj^ j\^^ \eiisi I have not found satisfactory evidence that they 

 St • ■ ht ®^®°* ^'^y artificial barrier over the entrance to their tunnels. 

 Burrow. ^ more complicated burrow and one better serving for defense 



is that of Leptopelma cavicula of northern Africa. The drawing 

 (Fig. 343) shows a section view of the upper part of the burrow, the en- 

 trance to which is without any door or other defense as in the case of the 

 tarantulas. Tlie burrow descends perpendicularly for a little ways, but at 

 the top a special branch diverges laterally, which curves and again descends 

 perpendicularly for a considerable distance. At the summit of this second 

 and parallel perpendicular tube another branch issues, inclining upwards 

 towards the surface. A glance at this structure, if we suppose it to be 



' Lucas, Hist. Nat. dos Aniinaux Crust, et Arach., page 357. 



^ Extrait dcs Annales de la Soci6t6 Entoniologique de France, "Arachnidcs du Vene- 

 zuela," December, 1887, April, 1888, pages 170-220, plates i., ii., iii. 

 " Actes de la Soci6t6 Linn^enne de Bordeaux, Vol. XLII., 1888. 



