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In all these rudimentary living coelenteria the sexual cells of both kinds ova and sperm cells are formed by the same individual; it is possible that the oldest gastraeads were hermaphroditic. The sexual cells originally proceeded from the edge of the primitive mouth of the gastraead.
When these are closed they resemble the Physemaria. Possibly the gastraeads that we call Physemaria are only olynthi with the pores closed. Prophysema primordiale, a living gastraead. The same in longitudinal section. Ascula of gastrophysema, attached to the floor of the sea. Olynthus, a very rudimentary sponge. The lowest form of the Cnidaria is also not far removed from the gastraeads.
There are not very many species of these living gastraeads; but their morphological and phylogenetic interest is so great, and their intermediate position between the Protozoa and Metazoa so instructive, that I proposed long ago to make a special class of them. But we might also regard these three orders as so many independent classes in a primitive gastraead stem.
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