The spinning-glands, u, lie above the spinnerets, and along the under side of the abdomen. They will be more fully described in the chapter on spinning.
POISON-GLANDS.
The poison-glands, n, are partly in the basal joints of the mandibles, and partly in the head, and discharge by a tube which opens at the point of the claw of the mandible, [Fig. 15], a.
CLASSIFICATION.
There is not room in this book to explain the classification of spiders into genera and species; but a description of the following well-marked groups, which contain nine-tenths of all spiders, will give a general idea of the differences among them, and help to understand what follows.
Fig. 6.
MYGALIDÆ
This family includes the largest known spiders. The body is usually very hairy and dark-colored. Most species have only four spinnerets; and one pair of these are long, and are turned up behind the abdomen. They have four air-sacs under the front of the abdomen, instead of two, as other spiders. Their mandibles are very large, and work up and down, instead of sidewise. The eyes are collected together on the front of the head. They live only in warm countries. Specimens from South America are exhibited in every natural history museum. [Fig. 6] represents Mygale Hentzii, a species living in Arizona and Texas.