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In others the plant-principle reappears; the worm-like creature retires from the free-moving life, attaches itself to a fixed base, and becomes the Bryozoan or the Echinoderm. To trace the development of these types in any detail is impossible. The early remains are not preserved.

His time has some value, if yours has not; and he has therefore educated his eye till it has become microscopic, like a naturalist's, and can classify nine out of ten specimens by one glance at a scale or a feather. Fancy an ambitious echinoderm claiming a private interview with Agassiz, to demonstrate by verbal arguments that he is a mollusk!

A plant may throw off bulbs, but these, sooner or later, give rise to seeds or spores, which develop into the original form. A polype may give rise to Medusae, or a pluteus to an Echinoderm, but the Medusa and the Echinoderm give rise to eggs which produce polypes or glutei, and they are therefore only stages in the cycle of life of the species.

At this period the embryo is partially organized, having faint traces of segments, and is still enveloped in its embryonal membranes and retains its connection with the shell. In an analogous manner the deciduous, pluteus-condition of the young Echinoderm perishes and is absorbed by the growing body of the permanent adult stage.

And, as a question of development, the formation of the radiate Echinoderm within its vermiform larva seems to me to be analogous to the formation of a radiate Medusa upon a Hydrozoic stock. But a Medusa is surely not the result of the coalescence of as many organisms as it presents morphological segments.

If a Bipinnaria, a Brachiolaria, a Pluteus, is competent to produce the Echinoderm, which is so widely different from it; if a hydroid polype can produce the higher Medusa; if the vermiform Trematode 'nurse' can develop within itself the very unlike Cercaria, it will not appear impossible that the egg, or ciliated embryo, of a sponge, for once, under special conditions, might become a hydroid polype, or the embryo of a Medusa, an Echinoderm."

Professor Haeckel adduces the fossil Crossopodia and Phyllodocites as examples of the Annelidan forms, by the coalescence of which the Echinoderms may have been produced; but, even supposing the resemblance of these worms to detached starfish arms to be perfect, it is possible that they may be the extreme term, and not the commencement, of Echinoderm development.

In the same way certain of the higher Radiates undergo all their transformations, from the Polyp phase of growth to that of Acaleph or Echinoderm, after birth; while others pass rapidly through the lower phases of their existence within the egg, and are born in their final condition, when all their intermediate changes have been completed.

The rocks which are composed of their remains show that vast areas of the sea-floor must have been covered with groves of sea-lilies, bending on their long, flexible stalks and waving their great flower-like arms in the water to attract food. With them there is now a new experiment in the stalked Echinoderm, the Blastoid, an armless type; but it seems to have been a failure.

If a Bipinnaria, a Brachialaria, a Pluteus, is competent to produce the Echinoderm, which is so widely different from it; if a hydroid polype can produce the higher Medusa; if the vermiform Trematode 'nurse' can develop within itself the very unlike Cercaria, it will not appear impossible that the egg, or ciliated embryo, of a sponge, for once, under special conditions, might become a hydroid polype, or the embryo of a Medusa, an Echinoderm."