B, C. multicornis, natural size; p, polyp; gon, gonophores; rh, hydrorhiza.
Dz, by the hydranths, each with dactylozoid; gz, gastrozoid; b, mouth and tentacles; and, blastostyle; gon, gonophores; secondly, the " coenosarc," or rh, hydrorhiza.
In some cases both free medusae and gonophores may be produced from the same hydroid colony.
This is the case in Syncoryne mirabilis (Allman , p. 278) and in Campanularia volubilis; in the latter, free medusae are produced in summer, gonophores in winter (Duplessis ).
The gonophores of different hydroids differ greatly in structure from one another, and form a series showing degeneration of the medusa-individual, which is gradually stripped, as it were, of its characteristic features of medusan organization and finally reduced to the simplest structure.
The next step is illustrated by the female gonophores of Cladocoryne, where the radial and ring-canals F G H Modified from Weismann, Entstehung der Sexualzellen bei den Hydromedusen.
- Diagrams of the Structure of the Gonophores of various Hydromedusae, based on the figures of G.
The hydroid Dicoryne 'is re- ' markable for the possession of gonophores, which are ciliate and become detached and swim away by means of their cilia.
It has been maintained that the gonads of Hydra represent sporosacs or gonophores greatly reduced, with the last traces of medusoid structure completely obliterated.
- Gonophores of Dicoryne conferta.
And can only be explained on the theory that gonophores are degenerate medusae, and is inexplicable on the opposed view that: medusae are derived from gonophores secondarily set free.
If we accept the view that Hydra is a true sexual polyp, and that its gonads are not gonophores (i.e.
Huxley, the sporosac is the starting-point of an evolution leading up through the various types of gonophores to the free medusa as the culminating point of a phyletic series.
The evidence against this view may be classed under two heads: first, comparative evidence; hydroids very different in their structural characters and widely separate in the systematic classification of these organisms may produce medusae very similar, at least so far as the essential features of medusan organization are concerned; on the other hydroids closely allied, perhaps almost indistinguishable, may produce gonophores in the one case, medusae in the other; for example, Hydractinia (gonophores) and Podocoryne (medusae), Tubularia (gonophores) and Ectopleura (medusae), Coryne (gonophores) and Syncoryne (medusae),-and so on.
If it is assumed that all these genera bore gonophores ancestrally, then medusa of similar type must have been evolved quite inde pendently in a great number of cases.
Hence it may be concluded that the gonophores are degenerate medusae, and not that the medusae are highly elaborated gonophores, as the organ-theory requires.
Gonosome with free medusae or gonophores; medusae usually with ocelli, never with otocysts.
When sessile gonophores are produced, they may show all stages of degeneration.
Trophosome arborescent, with hydranths of Bougainvillea-type; gonosome free medusae or gonophores, the medusae with solid tentacles in tufts (lophonematous).
Other hydroids are Garveia, Bimeria, Eudendrium and Heterocordyle, with gonophores, and Dicoryne with peculiar sporosacs.
Trophosome, polyps with scattered filiform tentacles; gonosome, medusae or gonophores, the medusae with hollow tentacles.
5), a common British hydroid, produces gonophores; so also does Cordylophora, a form inhabiting fresh or brackish water.
Coryne, a common British longed into a brood pouch conhydroid, produces gonophores; taining embryos.
Gonosome with free medusae or gonophores; the medusae typically with otocysts, sometimes with cordyli or ocelli (figs.
The blastostyles, gonophores and gonothecae furnish a series of variations which can best be considered as so many stages of evolution.
- The gonophores are reduced in varying degree, it may be to sporosacs; they are budded successively from the blastostyle, and each in turn, when ripe, protrudes the spadix.
- Trophosome as in the preceding; gonosome, free medusae or gonophores, the medusae with large open otocysts.
(From Moseley.) irregular coenosarcal canals, the coenosteum may contain, in its superficial portion, chambers or ampullae, in which the reproductive zoids (medusae or gonophores) are budded from the coenosarc.
In the Stylasteridae sessile gonophores are formed, always by budding from the coenosarc. In Distichopora the gonophores have radial canals, but in other genera they are sporosacs with no trace of medusoid structure.
Gonostyles, appendages which produce by budding medusae or gonophores, like the blastostyles of a hydroid colony.
Gonophores, produced either on the gonostyles already mentioned or budded, as in hydrocorallines, from the coenosarc, i.e.
The most usual condition, however, is that in which sessile medusoid gonophores or sporosacs are produced.