HORSESHOE-CRAB . 



295 



It lives on sandy and muddy shores below low-water mark, where it bur- 

 rows 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 nip- 

 pers, which are peculiar to the males. Sometimes the female is ac- 

 companied 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 espe- 

 cially interesting from the fact 

 that it is the last survivor of 

 an otherwise extinct group of 

 animals. Its relationships with 

 classes which have become ex- 

 tinct, its nearest relatives being 

 fossils, make it difficult to class- 

 ify 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 spi- 

 ders. It has the characteristics 

 of both groups. There are only 

 two known species of Limulus 

 in the world ; the other, Litnu- 

 lus moluccanus, lives on the 

 eastern coast of Asia. L. poly- 

 phemus often measures a foot in 

 diameter. The body is com- 

 posed 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 ab- 

 domen, 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. 



Under surface of horseshoe-crab, Limulus poly- 

 phemus : a, abdomen ; c, cephalothorax ; g, the first 

 gill-bearing abdominal appendage ; ra, mouth ; o, 

 operculum ; p, telson ; s, metastoma ; 1-6, cephalo- 

 thoracic limbs. 



