. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 202 PAUL E. FELL Gametogenesis and embryonic development in Haliclona loosanoffi are virtually identical to these processes in Haliclona ecbasis which has been studied in detail (Fell, 1969, 1970). The sperm develop within spermatic cysts which are scattered throughout the endosome. Each cyst is made up of one or more clusters of spermatogenic cells surrounded by a layer of pinacocytes. All of the cells of a cluster are at the same stage of development, but different clusters within the same cyst may be at different stages.
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 202 PAUL E. FELL Gametogenesis and embryonic development in Haliclona loosanoffi are virtually identical to these processes in Haliclona ecbasis which has been studied in detail (Fell, 1969, 1970). The sperm develop within spermatic cysts which are scattered throughout the endosome. Each cyst is made up of one or more clusters of spermatogenic cells surrounded by a layer of pinacocytes. All of the cells of a cluster are at the same stage of development, but different clusters within the same cyst may be at different stages. The sperm have a spherical head approximately 1 /j. in diameter and a tail about 10 ju, in length. All of the sperm in a cluster are oriented in the same direction. Frequently all stages of spermatogenesis occur simultaneously in the same specimen. The oocytes are individually distributed throughout the endosome. At an early stage of growth an oocyte becomes surrounded by nurse cells which it pro- gressively engulfs. The nucleus of the engulfed nurse cells disappears but the cytoplasm appears to remain unchanged. Consequently the larger oocytes and early embryos are filled with a large number of nurse cells, and little oocyte (or blasto- mere) cytoplasm can be discerned. After the engulfment of nurse cells is complete, the oocyte becomes enclosed within a thin follicular envelope consisting of flattened pinacocytes. Distinct blastomeres usually are not detectable during the initial cleavage stages, presumably because of the close packing of the cells. The early embryos are therefore difficult to distinguish from the larger oocytes at low magnification. As cleavage proceeds the engulfed nurse cells are gradually fragmented and incor- porated into the cytoplasm of the blastomeres. When this process is complete, the embryo develops into a solid, flagellated larva (parenchymula). Spicules appear at the periphery of the embryo during late cleavage, but as the larva develops they bec
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