Ernst J. Dornfeld

The fine structure of spermatid differentiation in the mussel, Mytilus edulis

In early spermatids of Mytilus edulis proacrosomal vesicles arising from several Golgi bodies coalesce to form one acrosomal vesicle. This moves to the anterior surface of the nucleus and invaginates to become an elongated cone-shaped structure. Membranoid sleeve material, also arising from Golgi elements, adjoins the acrosomal vesicle and later occupies its indentation. A fibrous axial rod extends posteriorly into the nucleus and anteriorly into the cavity of the acrosomal vesicle. Endoplasmic reticulum of early spermatids is predominantly free of ribosomes and by late spermiogenesis disappears. In early spermatids, nuclear chromatin forms peripheral aggregates and irregular filaments. Subsequent coalescence of chromatin masses forms a compact and barrel-shaped sperm nucleus. By mid-spermiogenesis the ellipsoid mitochondria become localized around and intimately apposed to the nucleus. The mitochondria become spheroid and reduced to five in number. Two cylindrical centrioles near the base of the nucleus are surrounded by the mitochondria of the middle-piece. The proximal centriole, oriented obliquely to the elongated distal centriole, retains its initial structure.

The effect of crustecdysone on DNA synthesis in polyploid somatic cells of an isopod

Abstract 1. 1. The effect of exposure to crustecdysone, in vivo and in vitro, on DNA synthesis in several polyploid tissues of the marine isopod Idothea wosnesenskii was determined by cytospectrophotometry and autoradiography. 2. 2. Injection of 0.02 mg hormone per mg body weight has no effect on relative DNA content or tritiated thymidine incorporation. 3. 3. Crustecdysone stimulates DNA synthesis in explants of testis sheath cells exposed to the hormone in vitro. 4. 4. Hepatic cecum and midgut cells do not synthesize DNA in response to crustecdysone.

Somatic polyploidy in the marine isopod Idothea wasnesenskii

Abstract 1. 1. The level, range, distribution and development of somatic polyploidy was studied in tissues in the marine isopod Idothea wasnesenskii . 2. 2. Extremely large nuclei were found in cells of the hepatic ceca (16C to 256C) and midgut (32C to 256C). 3. 3. The distribution of nuclear DNA values of these tissues suggests that ploidization does not occur by periodic doubling of genome. 4. 4. Nuclei of testis sheath cells, however, do form a doubling series of 8C, 16C and 32C nuclei with relatively few interclass values. 5. 5. Autoradiographic evidence indicates that adult testis sheath nuclei continue to synthesize DNA, while adult hepatic cecum and midgut nuclei do not. 6. 6. In juvenile specimens, polyploid nuclei in all three tissues synthesize DNA.