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Rh are to be found at its further extremity mounting guard over their egg-cocoon. Other species again live in trees, and spin a silken domicile either between forked branches or in the hollow trunk, or in large leaves rolled up for the purpose. There is no doubt that their food consists almost wholly of insects of various kinds. Nevertheless cases are on record of the destruction of small reptiles, mammals, and birds by these monstrous Spiders.

The discovery of stridulatory organs in the members of this family dates back to the year 1876, when Prof. Wood-Mason came across one in an Assamese species now known as Musagetes stridulans. Since that year organs like that which he described have been found, not merely in the solitary species as he and most of his successors appear to have thought would be the case, but in a great number of genera ranging from India to Queensland. For the proper comprehension, however, of the mechanism of this and the other organs of like nature described in this paper, it is necessary to add a few words in explanation of a spider's external anatomy. The fore part of the body, the part namely that lies in front of the waist, and is termed the cephalo-thorax, is furnished with six pairs of appendages arranged radially round its margin. The first appendage on each side, known as the mandible, consists of a short stout basal segment, covered above with hair and furnished below with a thick fringe of bristles, called, from its proximity to the mouth, the oral fringe (Fig. 1, c). Articulated to the tip of this basal segment is the second segment, modified to form a long stout pointed fang (Fig. 1, a). Behind the mandible on each side comes a short leg-like appendage called the palp, and consisting of six segments, of which the basal is usually termed the maxilla, from its function as a chewing organ. Its inner surface is furnished above with a suture, and below with an oral fringe (Fig. 2, B). Following the palp are the four walking legs, each of which is composed of seven segments, the basal being known as the coxa, and the second, like the second segment of the palp, as the trochanter.

Now these appendages are so arranged that their coxæ, and to a lesser extent their trochanters, are in contact with the corresponding segments of the appendange in front or behind; so that when a limb is raised upwards the adjacent surfaces of the segments in question slide over one another. These surfaces