. The Cambridge natural history. Zoology. 174 PORIFERA â ^ s morphosis in sea water which is constantly changed, and will live for some days. We have said that the young sponge has only one osculum. This is the only organ which is present in unit number, and it is natural to ask whether perhaps the osculum may not be taken as a mark of the individual; whether the fistular specimens, for example, of H. panicea may not be solitary individuals, and the cockscomb and other forms colonies in which the individuals are merged to different degrees. Into the metaphysics of such a view we cannot enter h
. The Cambridge natural history. Zoology. 174 PORIFERA â ^ s morphosis in sea water which is constantly changed, and will live for some days. We have said that the young sponge has only one osculum. This is the only organ which is present in unit number, and it is natural to ask whether perhaps the osculum may not be taken as a mark of the individual; whether the fistular specimens, for example, of H. panicea may not be solitary individuals, and the cockscomb and other forms colonies in which the individuals are merged to different degrees. Into the metaphysics of such a view we cannot enter here. We must be content to refer to the views of Huxley and of Spencer on Individuality. But it is advisable to avoid speaking of a multi- osculate sponge as a colony of many individuals, even in the sense in which it is usual to speak of a colony of polyps as formed of individuals. The repetition of oscula is probably to be regarded as an example of the phenomenon of repetition of parts, the almost universal occurrence of which has been emphasised by Bateson.^ Delage^ has shown that when two sponge larvae fixed side by side fuse together, the resulting product has but one osculum. This, though seeming to bear out our point of view, loses weight in this connexion, when it is recalled that two Echinoderm larvae fused together give rise in a later stage to but one Fig. 69.âLarva of Gellius varius shortly after fixation. The pigmented pole, originally posterior, is turned towards the reader. li, Marginal membrane with pseudopodia ; x, hinder pole. (After Maas.) Ephydatia fluviatilis. In the fresh water of our rivers, ponds, and lakes, sponges are represented very commonly by JEpliydatia (Spongilla) fluviatilis, a cosmopolitan species. The search for specimens is most likely ^ Materials for the Study of Variation, 1894, p. 30. 2 Arch, de Zool. Exp. (2) x. 1892, pp. 345-498. On the general subject, of adhesion of species, see Bowerbank, Brit. Ass. Rep. 1857, p. 11, wh
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