Page:The New International Encyclopædia 1st ed. v. 12.djvu/418

* LOBSTER. 370 LOBSTER. penetrated by a slit llirough vhicli pass water aiiJ minute grains of sand, which perform the function of otolites or lliu earl)ones of man. Waves of sound impinge on the ear, the grains of sand shake about, and the vibrations are transmitted to the sensitive feathery hairs, thcnee to the nerves, which unite to form the auditory nerve given oil from the complicated brain, which is situated under the solid rostrum or beak. Tlic sense of smell is evidently acute and is lodged in little olfactory rods arising from the joints of the outer Ihigella of the first pair of antennie. As in insects and other animals, it is this sense which directs them to their food, 1-atlicr than that of sight or even touch, the latter sense residing in the delicate hairs fringing the mouth and other head-appendages. Lobsters are sensitive to light, and are much more active at night than by day, seeking food or their mates in the darkness. IIawts. The food of the lobster is living as well as dead fish, the usual bail for lobster-traps being fresh dead lish. The food is comminuted in the fore-stomach ( provcntriculus), which is very large ami capacious, and at the posterior end the opening into the intestine is lined with a few very large teeth which serve as a strainer, through which the food presses into the long straight intestine, which opens externally on the under side of the telson. Lobsters are known to live on snails, breaking off the shell of large ones piece by piece and picking out the soft parts, or swallowing small ones whole. It is known that crabs are very active and will if transported several miles from their original habitat find their way back. .several lots of lobsters marked with a tag were liberated at Woods Hole, ilass., after they were stripped of their eggs. They all moved toward the south- west. One made the journey from Woods Hole to Cuttyhunk. a distance of 12 miles, in three days. One traveled 10 miles in twenty-seven days. A number returned to their original habitat at Cuttyhunk. Whether this forced mi- gration is due to the so-called 'homing instinct,' or that they are impelled to seek cooler water, remains to be seen ; none moved northward up Buzzard's Bay into the warmer waters. As is well known, the lobster can shoot backward to a considerable distance by su<ldenly flexing the abdomen under the cei)halothorax, going aceord- ijig to Herrick "25 feet in less than a second." The geographical range of the lobster i^ from Henley Harbor. Labrador, at the eastern mouth of the straits of Belle Isle, southward to Dela- ware Bay. though stragglers have been found off Cape Hatteras in thirty fathoms, and at Beau- fort, N. C. They have been captured on the fishing banks of the bays of Mame and Nova Scotia, and have been taken from the stomachs of cod caught on George's Bank. They are xisually, however, found near rocky shores lielow low-water mark to a depth of 10 to 20 fathoms: toward winter they migrate into water from 3o to 40 fatlioms deep. Large innoi)t:CTioN AND Breehjing Habits. Th.- ovaries ('coral') and corresponding male ghuKK are voluminous organs, the testes being while-, and the ovaries, when the lobster is al)Ovit to spawn, being pale green, and the ovarian eggs quite distinct. The eggs pass out of an opeiiiiiL' on the basal joint of each of the walking leg^ of the second pair: Ihe seminal ducts in the mal. open on the basal joint of each of the last or lil; i pair of legs. Pairing has never been observcil. I)ut it is known to take place in spring and summer. The breeding season is in July an.l August, though the eggs may be laid in tli spring or autumn, and even in winter. The egj are extruded and carried on the under side ui the body attached by a cement in bunches to tho hairs of the swimming legs, the process takiiiu place most probably in the night or early morn ing. The number of eggs laid is estimated 'o vary from 5000 to 80,000, and in some cases even to 100,000. The average number of eggs laid by a lobster eight inches long, when sexually ma- ture and 'in berry' or carrying eggs, is 5000 ; a ten-inch lobster bears about twice as many egg-^, and one of 12 inches carries double the number borne by one which measures 10 inches. When tlu' fourteen to sixteen inch limit is reached there i- a decline in sexual vigor. Female lobsters In- come sexually mature when from eight to twelxo inches in length. The variation in the number of eggs borne by lobsters of the same length is often very great. Embryology and Metamorpiicsis. The lob- ster has a much shorter larval life than most decapod Crustacea, and its development is in fact direct, its metamorphosis being incomplete. The period of incubation at Woods Hole is about ten months, from the middle of July or .iigust to the mi<ldle of the following ^lay or June. In one ease the eggs were carried .3.S5 days, from .July 1, 1800, to June 1. 1891. The yolk segments in about twenty-four hours after oviposition. and the embryo passes through the nauplius condition in ten days, and when from 26 to 28 days old the eye-pigment can be seen at the surface. The process of hatching for all the eggs borne by one female requires about a week. The young on hatching are driven away by the fanning motion of the parent, and in 5I;iy. .June, and .July they abound at the surface. During this time and until the fourth stage is reached im- mense numbers are devoured by stirfaccswliii- niing fish and other animals. Herrick states that a survival of two in every 10.000 larvne hatched would maintain the species at an equilibrium, and the destruction of the young under the pres- ent conditions of the fishery is probably even greater than this implies. After hatching, the young lobster passes through three stages before assuming the adult shape. In the first stage ( Fig. 1 ), which lasts from one to four or five days, the length of the body being a little ovm- a third of an inch (7.84 mm.), there are n^i abdominal appendages, and the two pairs .t antenna; are short and thick. It now differ-, however, from the larva (zoea) of most shrimps and crabs, in having the full complement of ■ thoracic legs. In the second stage, which lasts from two to five days, the length being 9.2