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Updated: May 26, 2025
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."
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."
When these ciliated larvæ are developed, they contract themselves so as to form a cavity; and this fifth stage especially important for his theory he calls gastræa. The importance of the eighth and ninth stages for the theory, we have already pointed out in our remarks upon Darwin, p. 43.
These ciliated chambers are easily detected in the sponge by means of a microscope, as they appear more highly colored. After the lecturer had thus given a general outline of the structure of the sponge, he drew attention to the character of its food and its method of digestion.
We have only to consider the first two of these classes; the other two are parasites, and have descended from the former by adaptation to parasitic habits and consequent degeneration. Their oval body, without appendages, is sometimes spindle-shaped or cylindrical, sometimes flat and leaf-shaped. Their skin is merely a layer of ciliated ectodermic cells.
Such a simple tissue is called an epithelium or surface-limiting tissue, and the cells are known as epithelial cells. These are united by a very small amount of a cement substance which belongs to the proteid class of material. The epithelial cells, from their shape, are known as squamous, columnar, glandular, or ciliated.
The fully-formed body is a gelatinous ball, with its wall composed of thirty-two to sixty-four ciliated cells; it swims about freely in the sea. After reaching maturity the community is dissolved. Each cell then lives independently for some time, grows, and changes into a creeping amoeba. This afterwards contracts, and clothes itself with a structureless membrane.
R. HIRSUTUM. Alpine Rose. South Europe, 1656. Very near R. ferrugincum, but having ciliated leaves, with glands on both sides. R. hallense and R. hirsutiforme are intermediate forms of a natural cross between R. hirsutum and R. ferrugincum. They are handsome, small-growing, brightly flowered plants, and worthy of culture. R. INDICUM. Indian Azalea.
Except the margin, which is ciliated, it is entirely destitute of hairs. The number of eggs contained in one of the scales is enormous, amounting in a single one to 691. The eggs are of an oblong shape, of a pale flesh colour, and perfectly smooth. In some of the scales, the eggs when laid on the field of the microscope resemble those masses of life sometimes seen in decayed cheese.
Along the ventral side of the branchial sac runs a ciliated groove the hypobranchial groove which we have previously found at the same spot in the Amphioxus. The food of the Ascidia also consists of tiny organisms, infusoria, diatoms, parts of decomposed marine plants and animals; etc.
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