=Feather-stars (Crinoidea).=--The feather-stars or sea-lilies or crinoids (fig. 24), as they are variously called, differ from the other Echinoderms in having the mouth on the upper side of the central disc, and in the fact that all of the species are fixed, either permanently or for a part of their life, being attached to rocks on the sea-bottom by a longer or shorter stalk which is composed of a series of rings or segments. The central disc is small and the radiating arms are long, slender, sometimes repeatedly branched, and all the branches bear fine lateral projections called pinnulæ. Most of the feather-stars live in deep water and are thus only seen after being dredged up. They feed on small crab-like animals, and on the marine unicellular animals and plants. [Illustration: FIG. 24.--A crinoid or feather-star, _Pentacrinus_ sp. (After Brehm.)] CHAPTER XIX BRANCH VERMES:[8] THE WORMS THE EARTHWORM (_Lumbricus_ sp.). TECHNICAL NOTE.--Obtain live earthworms of large size, killing some in 30% alcohol and hardening and preserving them in 80% alcohol, and bringing others alive to the laboratory. The worms may be found during the daytime by digging, or at night by searching with a lantern. They often come above ground in the daytime after a heavy rain. Live specimens may be kept in the laboratory in flower-pots filled with soil. "They may be fed on bits of raw meat, preferably fat, bits of onion, celery, cabbage, etc., thrown on the soil." =External structure= (fig. 25).--Examine the external structure of live and dead specimens. Which is the ventral and which the dorsal surface? Which the anterior and which the posterior end? Note the segmented condition of the body; the number of _segments_ or _somites_, and their relative size and shape. Note absence of appendages such as limbs and the presence of _locomotor setæ_ (short bristles). How many setæ are there on each segment and what is their disposition? The _mouth_ is covered by a dorsal projection called the _prostomium_. The _anal opening_ is situated in the posterior segment of the body. The broad thickened ring or girdle including several segments near the anterior end of the body is the _clitellum_, a glandular structure which secretes the cases in which the eggs are laid. On the ventral surface of the fourteenth and fifteenth segments (in most species) are two pairs of small pores; two other pairs of small openings (usually difficult to find), one between segments 9 and 10, and one between segments 10 and 11, are present. All these are the external openings of the reproductive organs. [Illustration: FIG. 25.--Dissection of the earthworm, _Lumbricus_ sp.] Make drawings showing the external structure of the earthworm.