the fold itself, the female sexual organ opens, consisting of a transverse opening invisible to the naked eye, but clearly seen on using a lens and removing the fold under which it is concealed, by means of the point of a scalpel or of a pin. The posterior extremity of the anus presents four spinnerets, of which the two upper are much the longer, and composed of four easily seen joints, the lower very short. The feet are moderate, and the longest are of the length of the entire body when this is fully developed (quando è perfettamente sviluppato); of these the fourth pair are about a third longer than the first, the third of about the same length as the second, which is the shortest of all. The tarsi of these are armed with two small curved claws, and the third and fourth joint with many long, delicate, straight, and mobile spines, which in the first pair become fewer as they approach the last joint. The eyes are arranged in three lines, as they are represented in C, Plate I., Fig. 3, and of these the two last of the posterior line are white and glistening, the others brown. "Our _Mygale_ lives in tubular cavities, or burrows, which she excavates for herself in loose and friable soil, in walls made of volcanic earth, in shady places, and for the most part turned to the north or to the west, seldom to the south--hence cool and rather damp. The burrows do not exceed the length of a palm, eight lines at their widest part. For about the length of an inch the tube is funnel shaped, thence it continues of a nearly uniform magnitude. Its first direction is almost horizontal, then it rises continually, turning to the right or left, and sometimes makes zigzags. As the tubes are excavated in friable soil, she takes care to tapestry them inside with the same glutinous material of which the other races make their web, by means of which the burrows are made smooth on the inside, and to strengthen them in such a manner that even when the outer earthy part has become cracked, or been torn away by the action of the rain, they remain firm and fit to conceal their inhabitant. I have often found the tubes of web thus left exposed, as they are represented in Plate I., Fig. 4, situated in the cement of a wall, and among _Lycopodium denticulatum_, _Adiantum Capillus-Veneris_, _Marchantia polymorpha_, and other small plants. And it seems that the animal, perceiving the nature of the soil, takes care to reinforce the silken case, so much the more as she finds the earth less firm, and _vice versâ_. So that in burrows excavated in solid ground, with the exception of a little space close to the aperture, the nest is merely smoothed and daubed; while sometimes the spider constructs a tube so strong that it supports itself even when deprived of all the earth, the animal having had the foresight to attach it along the course of the clefts of the rock, or to the cement of the pieces of tufa in the wall, as represented in Plate I. They have often also a