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They became almost sessile, living generally buried in the mud and gaining their food, consisting mostly of minute particles of organic matter, by means of currents created by cilia covering the large curtain-like gills. Their muscular system disappeared except in the ploughshare-shaped "foot" used mostly for burrowing, and in the muscles for closing the shell.
The evidence suggests that both the free-moving and the stalked Echinoderms descend from a common stalked Archaean ancestor. Some primitive animal abandoned the worm-like habit, and attached itself, like a polyp, to the floor. Like all such sessile animals, it developed a wreath of arms round the open mouth.
Sessile animals have had a similar history. But these parasitic and sessile forms had already been hopelessly distanced in the race for life. Their presence cannot impede the leaders; indeed their survival is necessary to directly or indirectly furnish food for the better conformed. In the animal and plant world there is abundant room and advantage at the top.
It is a hardy biennial, with a thick stalk, from eighteen inches to four feet high, and with very peculiar large woolly and mucilaginous leaves, and a long flower spike with ugly yellow and nearly sessile flowers. The leaves are best gathered in late summer or autumn, shortly before the plant flowers.
If the leaves are sessile, the analogy with the teasels is complete, as shown, for instance, in a case of Cotyledon, a crassulaceous plant which is known to produce such cups from time to time. They are narrower than those of the teasel, but this depends, as we have seen for the "one-leaved" ascidium, on the shape of the original leaf.
This fact at once points to an analogy with the umbellate allies, and induces us to examine the insertion of the flowers more critically. In doing so we find that they are united at their base so as to constitute a sessile umbel. The scapes are not absolutely lacking, but only reduced to almost invisible rudiments.
And one day I caught Winnenap' drawing out from mid leaf a fine strong fibre for making snares. The borders of the iris fields are pure gold, nearly sessile buttercups and a creeping-stemmed composite of a redder hue. I am convinced that English-speaking children will always have buttercups.
It is generally sessile and solitary, and may grow into the interior of the skull, into the frontal sinus, into the cavity of the orbit or nose, or may fill up the external auditory meatus, causing most unsightly deformity and interference with sight, breathing, and hearing.
The succeeding pairs alternate with one another, so as to place their leaves at right angles. The leaves are thus arranged on the whole stem in four equidistant rows. On the normal stem of a teasel the two members of a pair are tied to one another in a comparatively complicated way. The leaves are broadly sessile and their bases are united so as to constitute a sort of cup.
H. mollis, so called from the soft white down with which the leaves are covered, grows about 4 feet high. Leaves large, ovate, and sessile; growth of the plant upright, with hardly any branches; flowers pale yellow, about 3 inches across, not very ornamental. Cultivated at Kew, whence I had it. H. giganteus grows 10 feet high; stem much branched and disposed to curve.
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