Grantia compressa

Abstract: The fertilization of a calcareous sponge is studied by means of the electron microscope, in Grantia compressa F.. The mature oocyte lies beneath the choanoderm; the carrier cell is applied to its surface, and the spermiocyst enters its cytoplasm. The ultrastructural study demonstrates two formations in this spermiocyst: (i) the ‘head’, surrounded by a lamellar envelope, consists mainly of a nucleus with ring-shaped chromatin; (ii) a large area with a periodic structure corresponding to the modified ‘middle piece’ or ‘mitochondrial body’ of other authors.

Abstract: Paragrantia waguensis Hozawa is reported from coastal reefs of the island of Okinawa. This rare species was previously known only from Central Japan, Mie Prefecture. It has peculiar apopylar tetractine spicules, so far unique among Calcarea. We present in situ images of the species and a full description including SEM images of skeletal structure and spicule complement. The status of Paragrantia as a separate genus of the family Grantiidae distinct from Grantia Fleming is confirmed on the basis of a morphological and molecular comparison with the European type species of Grantia, Grantia compressa (Fabricius).

Abstract: I THINK there can be little doubt that the Amœbae referred to by Mr. Orton in NATURE of November 27 are not independent organisms, but constituents of the sponge from which he obtained them. I have been working for some time past at the problem of the origin of the germ cells in the common Grantia compressa, and have often found the flagellate chambers of the sponge crowded with am“boid cells, which can sometimes be seen actually squeezing themselves through the layer of collared cells. According to my observations, these am“bocytes are immature germ cells—;oogonia and spermatogonia—and they can often be seen undergoing mitosis in the chambers. A similar phenomena has been described in Sycon by Jrgensen. Possibly the am“boid cells squeezed out from the gastral cavity of Sycon by Mr. Orton were either of the same nature or else metamorphosed collared cells. The latter are very readily detached from their proper position in the sponge, and may then put out pseudopodia and come to resemble Am“b, as has long been known.