湘西北志留纪胴甲鱼化石

本文记述了采自湘西北澧县石门水库附近秀山组上段隶属云南鱼目的 Shimenolepis graniferus gen. et sp. nov. 和 QuJinolepidae gen. et sp. indet. 化石,对含鱼层的时代也进行了讨论.     

宁夏、内蒙古的一些早白垩世珠蚌类

宁夏六盘山群上部和内蒙古赛汉塔拉组产出的珠蚌类化石为首次描述,其面貌与邻区相当地层产出的蚌类相似,前人将它们鉴定为Unio。现据它们的壳顶区缺双带构造、前假主齿乳头状并不呈“多”形排列和前闭壳肌痕内具树枝状构造等特征建立Ningxiaconcha gen. nov.。本文还对Pseudelliptio属及其模式种的含义作了补充修订;通过这些珠蚌类化石的对比,宁夏六盘山群和内蒙古赛汉塔拉组可与新疆吐谷鲁群中上部、辽西沙海组和阜新组、山东蒙阴群中上部、浙江寿昌组上段以及苏联、蒙古、德国韦尔登阶进行对比,其时代应归入早白垩世早期。     

Middle Ordovician reefs of Norway

The Middle Ordovician reefs of Norway were the first to develop in the western part of the Balto-scandian epicontinental sea and are the earliest coral-stromatoporoid reefs so far reported in Europe. Small patch reefs in the Steinvika Limestone, Langesund-Skien district, consist mainly of algae, echinoderms, corals and stromatoporoids. Bryozoans, molluscs, arthropods and brachiopods are also present. The reefs developed on pelmatozoan-rich substrates and are organically zoned, consisting of a pioneer community of stemmed echinoderms and sheet algae, a high-diversity intermediate community dominated by fasciculate corals and a low diversity climax community of massive corals and stromatoporoids. These communities are interpreted as the seral stages of an autogenic ecological succession. Small patch reefs are also present in the laterally equivalent Mjøsa Limestone, Toten and Nes-Hamar districts. These are organically very similar to those in the Steinvika Limestone and developed in an identical way. A large complex, consisting of several reefs, is also present in the Mjøsa Limestone. Unlike the reefs elsewhere, which developed within shallow inshore areas, this complex developed at the outer edge of the inshore shelf. The outstanding feature of the complex is the main reef forming the offshore limit which is totally dominated by stromatoporoids and lacks a sequential development. This is due to the influence of the harsher environment at the shelf edge.     

RNA synthesis during early embryogenesis of mass cultured highly synchronized coleopteran embryos

Summary Bruchidius embryos are shown to be well suited for biochemical studies during early embryogenesis. Mass cultivation is easy, and highly synchronized embryos can be obtained in large numbers (10⁴–10⁵ eggs). A method for in vivo incubation is described which allows the labelling of newly synthesized RNA. The kinetics of³H-ruidine uptake, phosphorylation and incorporation into RNA are presented. By autoradiography, the distribution of newly synthesized RNA is shown. Thereby, stage-specific differences were found in the labelling pattern of vitellophage nuclei, of blastoderm nuclei and of the nuclei of pole cells. The labelling of the cytoplasm remains weak until cellular blastoderm is formed. During late blastoderm and at gastrulation this label increases markedly. Gel electrophoresis of isolated RNA shows that at cellular blastoderm formation most of the label occurs in a region between 18 S and 7 S. Later on, at the onset of gastrulation, the³H-uridine incorporation found in isolated RNA is raised about 10 fold and rRNA synthesis becomes prominent. In a chase experiment, the processing of precursor RNA molecules into shorter RNA species, especially into mature rRNA and 5S RNA, is shown. The advantages of theBruchidius embryo for the biochemical analysis of early RNA synthesis and the regulation of rRNA synthesis in insect embryos are discussed.Dedicated to Professor Dr. Dr. h. c. Bernhard Rensch at the occasion of his 80th birthday     

Changes in spatial distribution pattern during the larval stage of the fall webworm,Hyphantria cunea drury (Lepidoptera: Arctiidae)

Summary The changes in spatial distribution pattern during larval stage of the fall webworm,Hyphantria cunea were quantitatively investigated in the field experimental populations. The female adult deposits eggs as a cluster and the hatchlings make a compact colonial-web. In this period, the all-or-none type mortality which is characteristic in gregarious insect species was occasionary recognized before spinning a compact colonial-web. Once making a compact colonial-web, the larvae feed the leaves in the colonial-web up to about 5th instar. In this period, the movement of larvae occurred due to the local food shortage in a colonial-web and the expansion of colonial-web. As the larvae developed, the colonial-web was separated into several small groups. These larvae began to disperse about 5th instar. In this period, the local food shortage seems to be an important trigger for the larval dispersal. The mean concentration of larvae on leaves abruptly decreased, and finally the larvae became solitary at the 6th or 7th instars. The dispersal process in later larval stage is not necessarily due to the complete food shortage. The dispersal prior to the occurrence of food shortage may be a safety mechanism to protect the larvae from the food shortage.     

Quantitative aspects of RNA synthesis in normal and lithium-treated embryos ofXenopus laevis

Summary The treatment ofXenopus early embryos with lithium chloride produces exogastruale — embryos which fail to gastrulate normally and in which the rates of cell division are reduced. In the present study estimations of incorporations of (5-³H) uridine and the specific activities of the 5-ribonucleotide precursor pools showed that exogastrulae have higher rates of RNA synthesis per cell than control neurulae. Sub-cellular fractionations showed that a greater proportion of labelled RNA was retained in the nuclei of exogastrulae than of neurulae, while neurulae showed a greater incorporation into polysomes.     

The earliest known estuarine bivalve assemblage, Lower Ordovician of northwestern Argentina

The oldest known estuarine bivalve assemblage is documented from the Lower Ordovician (upper Arenig-lower Llanvirn) Alto del Cóndor Formation, which crops out in the Cordillera Oriental of northwestern Argentina. This unit displays most of the diagnostic sedimentary attributes of estuarine environments. Biotic components include low-diversity trace fossils and a peculiar bivalve fauna consisting of the new genera Konduria, Pseudoredonia, and Pucamya, and the new species Redonia condorensis. This constitutes the earliest known occurrence of bivalves in brackish waters, suggesting that the capability of this clade to colonize estuarine environments developed early in their radiation.     

Ectodermal-mesenchymal interspace during the formation of the chick leg bud

Summary The ectodermal-mesenchymal interspace of the chick leg bud was studied at stages leading to the formation of the apical ectodermal ridge (A.E.R.) (stages 14 to 19 HH), using scanning and transmission electron microscopy. The main findings were: 1. a continuous basal lamina under the ectoderm; 2. extracellular fibrils interconnecting the basal lamina and mesenchymal cell processes; 3. an increase in the number of the fibrils during these stages, with the highest number under the A.E.R.; 4. branching mesenchymal cell processes that spread over the basal lamina, making contact with it in all stages. The morphology of the interspace and the changes in it suggest that extracellular material may be significant in the ectodermal-mesenchymal interactions in the limb bud.     

The latest Ordovician Hirnantia brachiopod fauna of Myanmar: Significance of new data from the Mandalay Region

A new, latest Ordovician brachiopod fauna is systematically described from the Hwe Mawng Purple Shale Member (Hirnantian) of the Naungkangyi Group of the Pa-thin area, Mandalay Region, Myanmar, revealing one of the most diverse representatives of the typical Hirnantia Fauna. Rhynchonelliformean, craniiformean and linguliformean brachiopods studied belong to 23 genera and a few indeterminate taxa, among which the most abundant genus Kinnella, along with the four common genera (Paromalomena, Pseudopholidops, Fardenia, and Dalmanella), and other genera (such as Cliftonia, Draborthis, Hindella, Hirnantia, Leptaena, Mirorthis, Plectothyrella, Skenidioides, and Xenocrania) are recorded for the first time. This high diversity Hirnantia Fauna represents an ecological differentiation within the benthos of the Sibumasu Terrane during the end Ordovician global crisis. The palaeoeco-unit named herein as the Kinnella-Paromalomena Association is assigned to lower BA3. This paper includes a taxonomic revision with the following conclusions: 1) Sinomena Zeng et al. and Yichangomena Zeng et al. are treated as junior synonyms of Eostropheodonta Bancroft; 2) Hubeinomena Zeng et al. is regarded as a juvenile form of Coolinia Bancroft; 3) Paramirorthis Zeng et al. is considered an immature growth stage of Mirorthis Zeng; 4) Shanomena Cocks and Fortey is treated as a junior synonym of Paromalomena Rong; 5) Scenidium? medlicotti Reed is redesignated as the type species of Kinnella Bergström to replace Hirnantia? kielanae Temple. The distribution of the Hirnantia Fauna in Myanmar, Thailand and western Yunnan of the Sibumasu Terrane highlights the distinctive nature of the Mandalay fauna, and the analyses of the Hirnantia Fauna and others of Sibumasu shows that Sibumasu was not located far from the South China and Lhasa palaeoplates during late Middle and Late Ordovician.