BILATERAL TENDENCIES AND HABITS IN THE TWENTY-RAYED STARFISH PYCNOPODIA HELIENTHOIDES (STIMPSON)

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Abstract
1. Pycnopodia is highly bilateral when moving about in its natural abode. It uses the same side always as anterior end. 2. During righting reactions, this same side almost always takes the initiative and the greatest number of rightings are made in that direction. Repeated rightings do not improve its speed. 3. It is hardly ever found on dry land; its movements are swift enough so that it keeps below the tidal mark; it moves swiftest when stimulated from within. 4. In this, it seems to be partly governed by its sense to the pressure of minimum depths. 5. Three prime causes effect its migratory habits, to wit: (1) sensitivity to light of a certain intensity; (2) search for food; and (3) the breeding impulse. During the breeding season it is neither negative nor positive heliotropic; for it moves up from deeper water to shallower water independently of the directions of the rays of light. After spawning, however, it seems to be positive heliotropic. 6. It is omnivorous; it is carnivorous. It feeds mainly on Gasteropoda, but also on Pelecypoda, other species of starfish, sea-urchins, crabs, sponges, kelps and algæ. 7. The female seems to have reached a more definite number of rays before maturity, than has the male (see Fig. 4). 8. Maturity is not entirely dependent on the size of the animal; i.e., the diameter varies: In immature up to 12 inches; in males from 10-16½ inches; in females from 10½-20 inches. The females are on the average larger than are the males.

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