186 LIFE, IN ITS INTERMEDIATE FORMS. 
Pulmonaria; tho Harvest-men and Mites to the latter, 
and are called Trachearia. 
We naturally associate Spidors with cobwebs, and the 
faculty of spinning threads from the hind part of the body 
is one of their most marked characteristics ; but all do 
not make webs, properly so called. In the south of Europe 
and in the West Indies, certain large Spiders belonging to 
the genus Ctenizci are called Trap-door Spiders, from their 
singular architectural instincts. The female excavates a 
burrow in soft earth, an inch in diameter, and six to ten 
inches in depth ; this is lined with a dense tapestry re- 
sembling paper, formed of her silk; and the mouth is 
closed with a circular door, formod of many layers of silk, 
with pellets of earth interwoven into the exterior, but 
which is so smooth on the interior, and so accurately 
formed, as to fit the orifice with the utmost accuracy ; 
while a hinge of silk at one part of the circumference 
allows the lid to be raised for the exit of the owner, when 
it closes by its own elasticity. 
Judging from specimens which we have examined in 
Jamaica, tho lid is always punctured with a number of 
holes, such as might be made by a very fine needle, which 
penetrate through the whole substance, the light being 
clearly seen through each hole. We have conjectured 
that the object of these orifices may be the admission of 
air and light into the cell, when the lid is tightly closed, 
for the comfort of the inmate. The Spider habitually 
resides in her well-built house, coming abroad to hunt, 
and retreating with her prey to the bottom of her domain. 
In the hot parts of the world, Spiders ( Mygale ) closely 
allied to these are found, which are often of immense size. 
