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SYNOPSIS. Trichosphaerium platyxyrum sp. n., a marine testate rhizopod, is described. The schizont is ∼ 67 /μm in diameter, sheathed with a membranous test of fibrils and matrix covered with thin, straight, blade-shaped calcitic spicules. The gamont is ∼ 63 μm in diameter with a membranous test devoid of spicules. The tests of both stages contain circular apertures through which extend short dactylopodia. Locomotion is by lobopodia. Both the schizont and gamont are multinucleate with a mean of 38 nuclei/schizont and 23/gamont. Observed reproduction in both is by binary fission with variations described for the gamont. The type locality is the reef flat of Heron Island, Great Barrier Reef, Australia. It is suggested, but not confirmed, that Schaudinn's description of the life cycle of Trichosphaerium sieboldi may be extended to other species of Trichosphaerium.

The effects of freezing, drying, high temperatures, or various combinations of these on the eggs of the fresh-water ostracode Heterocypris incongruens were studied. In addition, the fate of 2,662 eggs of known parentage and time of laying was followed for 125 days. The results of the environmental experiments show that the eggs remain viable after drying at both 22°C and 40°C, and after being frozen wet or dry at -18°C. Eggs maintained wet at 40°C did not hatch. The result of the known parentage experiment showed that H. incongruens produces two types of eggs; one type develops and hatches within 10 days of laying, and another remains dormant for varying periods of time after being produced. Both types of eggs may be produced by the same individual, although some individuals may produce only dormant eggs. No female produced only rapidly developing eggs. There is no discernible pattern in the production of the two egg types, and the production of dormant eggs does not depend on recognizable changes in environmental factors. Furthermore, neither the age of the parent nor the number of eggs produced by her affects the type of egg laid. Eighty-five percent of the eggs produced are dormant with only a few capable of hatching whenever conditions arc suitable for growth. For an animal living in temporary ponds and seeps this means that some eggs are always in effect monitoring the environment for suitable hatching conditions. If these conditions occur and do not persist long enough for the hatchlings to reach maturity, other eggs will still be viable and available for hatching when favorable conditions return again.

SYNOPSIS Trichosphaerium micrum sp. n., a marine testate rhizopod, is described. It is ∼ 36 μ in diameter, covered with acicular, hollow, blunt-ended calcite spicules, 1–3 μm in length, that lie flat in a fibrous sheath. The test is penetrated by circular semipermanent apertures through which extend short dactylopodia. Locomotion is by lobopodia which the organism uses to adhere to the substrate. It is multinucleate with an average of 9 nuclei/individual. The type locality is the shallow littoral of Big Pine Key, Florida. Spicules of other species are described and it is suggested that until more is known about the biology of the group, species classification in the order Trichosida be based on spicule structure and orientation, as well as the size of the organism.

SYNOPSIS. The composition of the test of Rosalina floridana (Cushman) was examined histochemically, and its structure was studied with the electron microscope by means of thin sections and carbon replicas. The test is composed of a thick organic lining overlain by one or more calcite layers bounded above and below by thin membranes. The membranes are fused to organic pore processes composed of coarse fibers that penetrate the calcite layers. The ***lining, consisting of coarse fibers matted into a laminated sheet, is considered a strengthening element of the test. The membranes covering each calcite layer are composed of fine, headed fibrils which in aggregate have a striated pattern; they are thought to be the crystal-nucleating agent during calcification and to form a protective covering for the previously deposited calcite layers. The pore processes, which are devoid of an internal entrance for cytoplasm, are considered to be points of attachment for the membranes; they tie the organic test components into a unified whole. The calcite layers and the chambers lack this unity, being separated from each other and from the preceding chambers by membranes so that there are no calcite-to-calcite boundaries between them. An organic, sievelike structure of undetermined function has been found in the foramina of chambers near the prolocular region of the test. Histochemical methods show that the lining contains proteins, polysaccharides, and unidentified substances; the membranes and the pore processes stain as a protein-polysaccharide complex free of other substances.

SYNOPSIS. The foraminifer Rosalina floridana builds a chambered, calcareous test which is periodically enlarged by the addition of new chambers. R. floridana begins to form a chamber by constructing an algal growth cyst which covers the dorsal side of the animal and is cemented to the substrate. The pseudopods that build the cyst coalesce to form a cytoplasmic template or anlage on which the chamber walls will be secreted. Electron micrographs reveal the anlage cytoplasm to be a “froth” of nearly empty vesicles which contain mitochondria, fibrillar material, and electron dense granules. The organic lining of the new chamber is secreted on the anlage by pseudopods extending thru it. After the organic lining is completed, cytoplasm from within the test flows into the forming chamber and forces the anlage cytoplasm out thru the new aperture. This “frothy” anlage cytoplasm forms a sheath over the dorsal surface of the test; while it is in place, a layer of calcite is deposited on the walls of the new chamber and over the rest of the test. When calcification is completed, the sheath breaks up and is incorporated into newly formed pseudopods as the foraminifer gradually moves out of the growth cyst and begins normal feeding. The production of vesiculated cytoplasm in normal pseudopods and in the anlage is viewed as a method of greatly increasing cytoplasmic volume with a resultant very small loss in cytoplasmic mass. In the anlage during the production of the organic lining the vesiculated cytoplasm apparently acts only as a support for the membranes being secreted by the pseudopods and presumably does not take part in the secretory process. This same cytoplasm forms the sheath that is present during calcification. The view is advanced that, altho the sheath could be active during calcification with the mitochondria within the vesicles actively transporting calcium to sites of crystal growth, its more probable function is to form a partition between the parts to be calcified and the environment. The foraminifer could then secrete CaCO3 from pooled reserves in the cytoplasm into the area between the sheath and the chamber membranes. The basal membrane is considered the nucleating agent during calcification and is responsible for the ordering of the crystals so their C axes are perpendicular to the surface of the chamber.

Observations on living ostracods (Heterocypris) show that instars one to four require one to two days between molts, and instars five to eight require two to three days between molts.Tracer experim...