[Illustration: Under surface of horseshoe-crab, /Limulus polyphemus/: /a/, abdomen; /c/, cephalothorax; /g/, the first gill-bearing abdominal appendage; /m/, mouth; /o/, operculum; /p/, telson; /s/, metastoma; 1-6, cephalothoracic limbs.] ^L. polyphemus^, the horseshoe- or king-crab. This well-known and curious animal ranges along the Atlantic coast from Maine to Mexico. [pg295] It lives on sandy and muddy shores below low-water mark, where it burrows beneath the surface. At the breeding season—May, June, and July—it comes ashore to deposit its eggs near high-water mark. The crabs come up the beach in pairs, the male being the smaller and riding on the back of the female, holding on by short feet provided with nippers, which are peculiar to the males. Sometimes the female is accompanied by several males, each one holding on to the tail of another and forming a string of animals. After the female has deposited her eggs in a hole excavated by her for the purpose, the male covers them with milt, and they then return to the water, leaving the eggs to be buried in the sand by the action of the waves. The eggs hatch in July and August, and sometimes the beach is literally alive with the young crabs, which, however, soon disappear, and are not seen again until they are well grown. After the spawning season the adults are not very often seen, but usually their empty shells, abandoned in moulting, may be found on the shore. The horseshoe-crab, also called king-crab, is especially interesting from the fact that it is the last survivor of an otherwise extinct group of animals. Its relationships with classes which have become extinct, its nearest relatives being fossils, make it difficult to classify definitely with existing forms. Formerly it was regarded as a crustacean; now it is classed by some authors with the /Arachnida/, along with scorpions and spiders. It has the characteristics of both groups. There are only two known species of /Limulus/ in the world; the other, ^Limulus moluccanus^, lives on the eastern coast of Asia. /L. polyphemus/ often measures a foot in diameter. The body is composed of three parts. The front portion, or cephalothorax, is broad and semicircular, with posterior angles ending in points. Near each side of its dorsal surface is a pair of large compound eyes covered with thickened cuticle, and near the center line of the shell, at the base of the first spine, a pair of small, simple eyes. The second portion is the abdomen, and the third a long, movable spine attached to the last segment of the abdomen and between two terminal points of the horn-like covering. [pg296] On the cephalothorax are seven pairs of appendages. The first pair are small and lie in front of the mouth; these and the four following pairs have chelæ, or claws. The sixth pair have no chelæ, but at the base have a peculiar process termed the flabellum.