The germ-cells are capable of extensive migrations, not only in the body of the same polyp, but also from parent to bud through many non-sexual generations of polyps in a colony (A.
- All known hydropolyps possess the power of reproduction by budding, and the buds produced may become either polyps or medusae.
Upon the polyps FIG.
After a time the polyps, or certain of them, produce by budding medusa-individuals, which sooner or later develop sexual elements; in some cases, however, the founder_ polyp remains solitary, that is to say, does not produce polypbuds, but only medusa-buds, from the first (Corymorpha, fig.
In this way the hydroid colony becomes composed of two portions of different function, the nutritive " trophosome," composed of non-sexual polyps, and the reproductive " gonosome," composed of sexual medusaindividuals, which never exercise a nutritive function while attached to the colony.
- Polyps from a Colony indicated in the case of the polyps of Hydractinia, magnified.
The hydroid colony shows many variations in form and architec- ture which depend simply upon differences in the methods in which polyps are budded.
From the stolon the daughter-polyps grow up vertically.
F, the founder-polyp; I, 2, 3, 4, the succession of polyps budded from the founder-polyp; a', b', c', the succession of polyps budded from 1; a 2, 2 polyps budded from 2; a 3, polyp budded from 3.
15),the polyps produce buds right and left alternately, so that the hydranths are arranged in a zigzag fashion, forming a " scorpioid cyme," as in Obelia and Sertularia.
F, foundersecond bud, which usually polyp; I, 2, 3, succession of polyps forms a side branch or pinnule budded from the founder.
Whereas primitively any polyp in a colony may produce medusa-buds, in many hydroid colonies medusae are budded only by certain polyps termed blastostyles (fig.
At first not differing in any way from other polyps (fig.
5), the blastostyles gradually lose their nutritive function and the organs connected with it; the mouth and tentacles disappear, and the blastostyle obtains the nutriment necessary for its activity by way of the coenosarc. In the Calyptoblastea, where the polyps are protected by special capsules of the perisarc, the gonothecae enclosing the blastostyles differ from the hydrothecae protecting the hydranths (fig.
- Diagram showing method polyps (fig.
One class g g of polyps, the dactylozoids of branching in the Plumularia-type; (dz), lose their mouth and compare with fig.
Such are the " guard-polyps " (machopolyps) of Plumularidae, which are often regarded as individuals of the nature of dactylozoids, but from a study of the mode of budding in this hydroid family Driesch concluded that the guard-polyps were not true polyp-individuals, although each is enclosed in a small protecting cup of the perisarc, known as a nematophore.
F, founder-polyp; 1, 2, 3, 4, 5, 6, succession of polyps budded from the founder; a, b, c, second series of polyps budded from the founder; a 3, b 3, series budded from 3.
It has been shown above that polyps are budded only from polyps and that the medusae may be budded either from polyps or from medusae.
The first case gives a colony entirely composed of polyps, as in many Hydroidea.
It is convenient to distinguish buds that give rise to polyps from those that form medusae.
The tissues of the bud become differentiated into ectoderm and endoderm, and the endoderm of the bud becomes secondarily continuous with that of the parent, but no part of the parental endoderm contributes to the building up of the daughter-polyp. Lang regarded this method of budding as universal in polyps, a notion disproved by O.
However, both of the statements and figures of Lang and of the facts to be described presently for medusae (Margellium), it is at least theoretically possible that both germinal and vegetative budding may occur in polyps as well as in medusae.
The life-cycle of the Leptolinae consists of an alternation of generations in which non-sexual individuals, polyps, produce by budding sexual individuals, medusae, which give rise by the sexual process to the non-sexual polyps again, so completing the cycle.
Founder-polyp) nor its offspring by budding (polyps of the colony) have the power of becoming medusae, but only of producing medusae by budding.
After I had learned a great many interesting things about the life and habits of the children of the sea--how in the midst of dashing waves the little polyps build the beautiful coral isles of the Pacific, and the foraminifera have made the chalk-hills of many a land--my teacher read me "The Chambered Nautilus," and showed me that the shell-building process of the mollusks is symbolical of the development of the mind.