Embriogenesis and larval ontogeny of the "piau-gordura", Leporinus piau (Fowler) (Pisces, Anostomidae) after induced spawning

Mature males and females of Leporinus piau (Fowler, 1941) were induced to reproduce through a hypophysation process. Extrusion occurred 12 h or 312 hours-degree after the hypophysation, at a water temperature of 26°C. Fertilized eggs were maintained in incubators at 24°C. Embryonic development, was evaluated using every 10 minutes, fresh egg samples which were analyzed under stereoscopic microscope. The larvae were collected at 24-hour intervals for seven days after hatching, fixed in Bouin's fluid and were submitted to routine histological techniques. The eggs of L. piau were slightly gray, non-adhesive and round-shaped. After 1.5 h the embryo was at the 64-blastomere phase and showed a wide yolk region on the vegetative pole. Within 6.25 h, blastopore closure and the end of gastrula was observed. The differentiation of layers occurred after 7.5 h and hatching after 21 h after fertilization at 24°C or 504 hours-degree. During the first three days of the larvae development there was a gradual yolk sac reduction until its complete absorption on the fourth day, indicating the necessity of exogenous feeding. From the fourth to the seventh day, the final development of the heart, gill arches, swimblader, kidney, hepatopancreas, stomach and intestine were observed. The embryonic and larval development of L. piau were similar to other Anastomidae species.

Pollen Development in Orchids. 5. A Generative Cell Domain Involved in Spatial Control of the Hemispherical Cell Plate

The unequal first pollen mitosis in moth orchids (Phalaenopsis) is followed by an unusual form of cytokinesis that isolates a small lens-shaped generative cell from a large vegetative cell. No preprophase band of microtubules predicts the division plane and the new cell plate grows completely around the generative cell rather than fusing with the parental wall. Development of the phragmoplast cytoskeleton consisting of fusiform bundles of microtubules and F-actin occurs in three major stages: (1) the initial asymmetrical phragmoplast conforming to the shape of the interzonal region, which tapers from the broad mass of chromosomes at the generative pole to the rounded mass at the vegetative pole; (2) the symmetrical plate-like phragmoplast; and (3) the hemispherical phragmoplast, which curves around the generative nucleus. Microtubules of the generative half of the hemispherical phragmoplast are nuclearbased, while those on the vegetative side terminate in endoplasmic reticulum. The path of the phragmoplast appears to outline a cytoplasmic domain denned by a radial system of microtubules emanating from the generative nucleus.

Observations on the origin of the ‘germinal cytoplasm’ in Xenopus laevis

The early appearance of the ‘germinal cytoplasm’ and its behaviour during the formation of cells which are thought to represent the primordial germ cells have been described in detail for Rana temporaria by Bounoure (1927, 1934, 1939) and Blackler (1958). These observations were extended to Xenopus laevis (Nieuwkoop, 1956; Nieuwkoop & Faber, 1956; Blackler, 1958), Bufo bufo (Blackler, 1958), Rana pipiens (Berardino, 1961), Discoglossus pictus (Gipouloux, 1962 a) and Rana esculenta (Hammer, cited by Blackler, 1965 b). The above findings agree with respect to the earliest detection of the ‘germinal cytoplasm’. Its first appearance was noticed as early as in the fertilized, unsegmented egg, where small, distinctly staining islands of cytoplasm are localized just under the cell membrane in an area around the vegetative pole of the egg. During cleavage the ‘germinal cytoplasm’ is distributed between the vegetative blastomeres directly surrounding the vegetative pole.

Analysis of follicle cell patterns in dextral and sinistral Limnaea peregra

Several experiments done in our laboratory make it likely that in the egg of Limnaea stagnalis there is a cortical morphogenetic field (Raven, 1949, 1952, 1966). One of us (Raven, 1963, 1964, 1967) has studied the origin of this morphogenetic field. In the newly laid egg cell there is a vegetative pole plasm, occupying a sector of about 110 degrees with its apex near the centre of the egg. It is situated somewhat obliquely with respect to the longitudinal axis of the first maturation spindle. Moreover, a circle of six lenticular subcortical patches of cytoplasm are found in the equatorial region of the egg. These ‘subcortical accumulations’ (SCA) are arranged according to a regular pattern. Four of them are situated close together on one side, occupying about 180 degrees of the egg circumference; two somewhat larger SCA lie on the opposite side. The SCA, together with the obliquity of the vegetative pole plasm, define a pattern.