TRAP-BOOR SPIDERS. 229 



plexity and subtlety of their contrivance, and, tliere- 

 fore, to the difficulty we experience in properly under- 

 standing- and describing them. 



It will be seen by a reference to Plate XIX.,* figs. 

 A and A 1, that in addition to the cylindrical branch, 

 which mounts upwards, there is a shorter branch 

 which leaves the main tube on the opposite side (on 

 the left as seen in the Plate), and takes a downward 

 course. Xow this descending branch, which is barely 

 more than an inch in length, is a cavity of variable 

 form, being sometimes cylindrical, and sometimes egg^ 

 or even watch-shaped, f but there is one particular in 

 which it never varies, and that is the position of its 

 elliptic orifice. This orifice is always situated on the 

 opposite side of the main tube to that on which the 

 ascending branch leaves this latter, so that the whole 

 nest, when seen in section, presents the figure 

 of a St. Andrew's cross, only with arms of unequal 

 length. 



But the most remarkable point is that, when the 

 lower door is pushed across so as to close the main 

 tube (as shown in fig. A, Plate XIX.), it will in- 

 variably be found to lie in such a position that its 

 lower extremity exactly meets the lower lip of the 

 orifice of the descending cavity, when it will be seen 

 that the semi-cjdindrical surface of the lower door 

 then coincides with, and appears to continue and 

 form part of, the lower wall of the descending cavity 



* A nest of a scarcely half-grown spider is here represented in order tliat 

 sufficient space might be gained to show the lower door in its two positions. 

 The perfect cavity is still found in nests of much larger dimensions, and occa- 

 sionally, indeed, in nests of almost the maximum size. 



+ I take the liberty of coining a word to replace "lenticular," the form of a 

 watch being more familiar than that of a lens. 



