The number of animals available at Woods Hole, Mass., varies from year to year; at times they are abundant, at other times they are very scarce. Mature females are recognizable by the presence of pale-pink or purplish gonads; the gonads of the males are milky-white. The animals are usually abundant in the spring, but disappear in July.

This is reported to extend from mid- to late summer.

A. Care of Adults: Aurelia is very difficult to maintain alive in the laboratory for any period of time; large aquaria, supplied with adequate amounts of running sea water, are probably desirable.

B. Methods of Observation: Eggs and developing planulae can be dissected from the brood-pouches located on the inner surfaces of the oral arms; they should be mounted in a drop of sea water for microscopic observation.

Active planulae, obtained in the above manner will readily attach and metamorphose as far as the scyphula stage, if they are placed in clean watch glasses of sea water. Gilchrist (1937) gives directions for culturing the scyphistoma stage.

A. Early Stages of Development The pinkish, transparent eggs measure about 120 microns in diameter. Fertilization occurs in the gastric pouches, and the eggs are transferred to small brood-pouches on the inner surfaces of the oral arms. Cleavage is total and quite regular, forming a hollow, single-layered blastula. Gastrulation is by invagination, occasionally accompanied by an in-wandering of cells. At the time of completion of the gastrulation process, the blastopore, which becomes the mouth of the scyphistoma, is almost completely closed. The spherical embryo develops cilia and elongates, taking on an egg-shape; the blastopore is located at the more pointed end. At this stage, the larva leaves the brood-pouch and takes up a free-swimming existence. For details of the early stages of development, see the papers by Hargitt and Hargitt (1910) and Smith (1891).

B. Later Stages of Development In about two days the planula attaches by the aboral end and gradually flattens to a cup-shape, losing its ciliation; it is now a young scyphistoma. The mouth and a short hypostome soon become visible. Four primary tentacles arise in a circle about the gaping mouth, and, alternating with these, four endodermal ridges (the taeniolae) project into the coelenteron. The tentacle number is increased to 24 in about a month. Lateral buds can be produced, which either become free or form stolons from which new scyphistomae arise. In the older scyphistomae, the gastric pouches can be seen to communicate by means of holes in the taeniolae, forming the ring sinus just below the oral disc. Sense organs are visible at the bases of each of the eight primary tentacles, appearing first as wart-like buds. Eight lobes from the ring sinus grow out as lappets towards the sense organs, each lappet eventually enclosing a sense organ in its forked tip. When this stage is reached, strobilization occurs. For details of scyphistoma formation, see the paper by Hein (1900).

C. Strobilization and the Ephyrula: The scyphistoma stage of Aurelia is long and strobilization does not usually occur until about April. At this time, the primary tentacles are lost and the tubular body is divided into a series of plate-like discs. Each of these discs becomes free as a small ephyrula, or young jelly fish. The ephyrula bears eight forked lappets, each of which is tipped with a sensory tentacle. The four gastric pouches, lined with gastric filaments which develop from the free edges of the original taeniolae, are clearly visible. Further growth over a period of four months leads to the formation of an adult jelly fish. Details of ephyrula formation and strobilization can be found in the papers by Friedemann (1902) and Percival (1923); the entire development of Aurelia is reviewed by MacBride (1914).

FRIEDEMANN, O., 1902. Untersuchungen uber die postembryonale Entwicklung von Aurelia aurita. Zeitschr. f. wiss. Zool., 71: 227-267.

GLICHRIST, F. G., 1937. Rearing the scyphistoma of Aurelia in the laboratory. In: Culture Methods for Invertebrate Animals, edit. by Galtsoff et al., Comstock, Ithaca, p. 143.

HARGITT, C. W., AND G. T. HARGITT, 1910. Studies in tile development of Scyphomedusae. J. Morph., 21: 217-262.

HEIN, W., 1900. Untersuchungen fiber die Entwicklung von Aurelia aurita. Zeitschr. f. wiss. Zool., 67: 401-438.

MACBRIDE E. W., 1914. Text-Book of Embryology. Vol. I. Invertebrata. Macmillan and Co., Ltd., London.

PERCIVAL, E., 1923. On the strobilization of Aurelia. Quart. J. Micr. Sci., 67: 85-100.

SMITH, F., 1891. The gastrulation of Aurelia flavidula, Per. & Les. Bull. Mus. Comp. Zool., Harvard, 22: 115-124.