The most primitive way of hunting in Mygalomorph spiders seems to be the free roaming and catching of encountered prey Theraphosidae. The trap-door spiders Ctenizidae, Actinopodidae and Barychelida which are entirely sedentary, lie in wait behind the trap-door and leap at prey that happens to pass close to the door. Some species spin radial silk threads outside the door which function as stumbleor signal-lines, and some Australian species use grass blades and other litter in the same way. A further evolutionary step leads to species which do not build a trap-door but crown their burrow by a funnel-shaped web. The Dipluridae finally are real web-builders, which depend on a sheet-web to catch their prey. Generally they do not dig a burrow but hide in a small retreat from which a funnel-web leads to the net. With a few exceptions Ctenizidae are entirely nocturnal. Their rhythm of activity has been analyzed. The “Zeitgeber” is the daylight during the last half hour before sunset. Most trapdoor spiders never leave their burrow during their whole life. They need three to four years from hatching to become adults. Adult males die during or at the end of the restricted mating-season; they take no food when adult. Females, which undergo post-adult molts, can probably live for 15–20 years. Nemesia caementaria, like most other species, hunts during the whole night. The mean time of activity is about Si/o hours, consisting of periods of lying in wait and periods of intermediate rests. The spiders make an average of three leaps per night to catch a prey, but only about 10% of all bounds are successful. A hungry animal, lurking in vain, shows unmotivated leaps. The effects of light, moisture, and temperature on hunting activity are analyzed. Ctenizidae hunt during autumn, winter, and spring but interrupt their activity in summer for an estivation which lasts usually two months. The females of some species capture the male after mating and eat him; others never attack him. This difference in behavior lias repercussions on reproduction. Among certain species the young nymphs of the third instar refuse all food until they have made their own burrow and can hunt by themselves. The young of other species stay with the mother for one year and leave her at the fifth or sixth instar to make their own burrow. The young of Nemesia caementaria can remain in the burrow of the mother until they are almost adult, i.e., for two or three years, and feed on the prey the mother has caught. The behavior of Ctenizidae can be grouped. Some species lurk behind the closed or almost closed trap-door. Another group opens the trap-door and puts the pedipalpi and the two anterior pairs of legs radially out onto the rim of the burrow, while the cephalothorax is hidden behind the trap-door. A third group spins threads of silk radially about the entrance and uses them as signal-lines. A fourth group can come out and pursue the prey, then drags it to the trap-door and into the burrow. The nature of the prey depends on the bio tope. The Ctenizidae feed almost exclusively on insects, mainly ants and beetles; in the laboratory crickets are accepted as prey. Ctenizidae have no tarsal organ. They have different types of trichobothria, transversal and longitudinal slit-organs, and lyriform organs. With these three kinds of sense-organs, the functions of which are not clearly understood, the trap-door spiders are able to perceive the approach of prey, to judge its distance from the trap-door, and to locate it in direction. They seem to have an organ of smell, since certain groups of insects are repulsive to them. Sight is not used for hunting.