The intranuclear spindle of yeast has an electron-opaque body at each pole . These spindle plaques lie on the nuclear envelope . During mitosis the spindle elongates while the nuclear membranes remain intact. After equatorial constriction there are two daughted nuclei, each with one spindle plaque . The spindle plaque then duplicates so that two side-by-side plaques are produced . These move rapidly apart and rotate so that they bracket a stable 0 .8 µm spindle. Later, during mitosis, this spindle elongates, etc . Yeast cells placed on sporulation medium soon enter meiosis . After 4 hr the spindle plaques of the more mature cells duplicate, producing a stable side-by-side arrangement . Subsequently the plaques move apart to bracket a 0.8 µm spindle which immediately starts to elongate . When this meiosis I spindle reaches its maximum length of 3-5 µm, each of the plaques at the poles of the spindle duplicates and the resulting side-by-side plaques increase in size . The nucleus does not divide . The large side-by-side plaques separate and bracket a short spindle of about 1 µm which elongates gradually to 2 or 3 µm . Thus there are two spindles within one nucleus at meiosis II . To the side of each of the four plaques a bulge forms on the nucleus . The four bulges enlarge while the original nucleus shrinks . These four developing ascospore nuclei are partially surrounded by cytoplasm and by a prospore wall which originates from the cytoplasmic side of the spindle plaque . Eventually the spore nuclei pinch off and the spore wall closes . In some of the larger yeast cells this development is completed after 8 hr on sporulation medium.

Wild-type Drosophila melanogaster were axenically raised on a completely synthetic fatty acid-free diet for at least ten consecutive generations, confirming that these insects do not require dietary polyunsaturated fatty acids. Capillary column gas-chromatographic analysis of lipids extracted from adults reared on yeast medium showed a peak which cochromatographed with linoleic acid, representing about 1.2% and 0.15% of all fatty acids in phospholipids and triacylglycerols, respectively. In flies reared on the synthetic diet for one generation or for five or more generations, the linoleic acid peak was still present but in about tenfold lower proportions of total fatty acids. This was true of both phospholipid and triglyceride fractions.

Exogenous juvenile hormone (JH) application to Schistocerca gregaria eggs interfered with normal embryogenesis in a dose- and age-dependent manner. Embryos treated between 3 to 9 days postoviposition were inhibited at (1) blastokinesis; (2) postblastokinesis; (3) as vermiform larvae; or (4) as first-instar hoppers unable to shed their provisional entitle completely. The development of 3- to 5-day-old embryos was inhibited at blastokinesis when the embryos were treated with 1 μg JH but not with 0.1 μg JH. However, sensitivity increased with age, so that 8-to 9-day-old embryos were unable to shed the provisional cuticle when treated with as low as 0.01 μg JH. Treatment of embryos later than 10 days after oviposition did not disrupt embryogenesis and did not result in postembryonic aberrations at any stage in the life cycle. Furthermore, exogenous JH treatment of developing embryos did not enhance solitarization of S. gregaria.Disruption of embryogenesis was accompanied by an increase in brown coloration of the embryos. Microscopic examination revealed an interference with the normal development of the provisional cuticle.

No abstract