1. Troglohyphantes cavernicola Keys. is found everywhere in these caves, where the three following necessary conditions exist—total darkness, a saturated atmosphere, and a suitable place for the construction of snares.2. The first pair of legs are used as tactile organs.3. All small winged insects, thysanurans and small myriopods serve as food. Scarcity of food does not entirely limit their distribution.4. They have no known enemies other than themselves.5. While temperature outside the caves does not materially affect the adult spiders themselves, it is probable that to the even temperature at localities between 600 and 1,700 feet from the entrance is due the great number of specimens found at this place.6. Courtship is similar to that of some outside forms.7. Cocooning is rudimentary. The eggs are few and comparatively large.8. The young are white and are thicker set than the adults. Some are hatched with eyes, while others are entirely blind.9. Moulting is comparatively rare and is often fatal. There a...