是胚胎还是藻类？：兼答薛耀松,周传明,唐天福先生

贵州瓮安陡山沱组磷块岩中所产的球状微体化石曾被薛耀松等 ( Xue et al.,1 995)解释为团藻类化石 ,最近被重新解释为早期动物休眠卵和胚胎化石 ( Xiao et al.,1 998)。薛耀松等 ( Xue etal.,1 998;下称薛文 )对动物休眠卵 -胚胎的解释提出六点不同看法 ,并坚持认为这些球状微体化石应为团藻类化石。本文对薛文中所提六点看法进行逐条解答 ,并着重讨论了球状微体化石的大小和丰度 ,磷酸盐化“细胞壁”,生物软体的磷酸盐化过程 ,以及团藻类的生理和生殖特点和陡山沱球状微体化石的不同特征。事实上 ,陡山沱组磷酸盐化动物休眠卵和现代某些甲壳类体眠卵在外表装饰上几乎雌雄难辨 ,陡山沱组球状微体化石的大小、发育过程、卵裂形式以及外层包膜的存在也和动物胚胎的解释相吻合。显然 ,动物休眠卵 -胚胎仍然是对陡山沱球状微体化石的最佳解释。     

新元古代磷酸盐化外包型腔原肠胚化石在瓮安生物群中的发现

贵州瓮安埃迪卡拉纪陡山沱组(635—551Ma)上磷矿段保存了丰富的磷酸盐化动物胚胎化石,其中绝大多数为早期卵裂胚胎化石,原肠胚化石相对罕见。文中报道瓮安生物群中新发现的一种类似现代两栖动物胚胎的外包型腔原肠胚化石,并依据新的三维立体胚胎化石标本对瓮安陡山沱组原肠胚期动物化石的多样性及其可能的亲缘关系进行初步探讨,认为:1)"外包型腔原肠胚"和已有轴性分化的"外包型实体原肠胚"的发现为证明瓮安生物群中存在两侧对称动物提供了新的化石证据;2)"单极内陷型腔原肠胚"因胚体存在巨大空腔(囊胚腔和原肠腔)而难以被磷酸盐化精细保存,故在瓮安生物群中的化石记录稀少且亲缘关系不明;3)瓮安生物群中的"单极内移型腔原肠胚"和"分层型腔原肠胚"化石的可靠性尚有待更多的标本提供佐证。瓮安生物群中颇具多样性的原肠胚期动物化石为探索后生动物在晚新元古代的胚胎发育模式开拓了思路。     

新元古代磷酸盐化外包型腔原肠胚化石在瓮安生物群中的发现北大核心

贵州瓮安埃迪卡拉纪陡山沱组(635—551Ma)上磷矿段保存了丰富的磷酸盐化动物胚胎化石,其中绝大多数为早期卵裂胚胎化石,原肠胚化石相对罕见。文中报道瓮安生物群中新发现的一种类似现代两栖动物胚胎的外包型腔原肠胚化石,并依据新的三维立体胚胎化石标本对瓮安陡山沱组原肠胚期动物化石的多样性及其可能的亲缘关系进行初步探讨,认为:1)"外包型腔原肠胚"和已有轴性分化的"外包型实体原肠胚"的发现为证明瓮安生物群中存在两侧对称动物提供了新的化石证据;2)"单极内陷型腔原肠胚"因胚体存在巨大空腔(囊胚腔和原肠腔)而难以被磷酸盐化精细保存,故在瓮安生物群中的化石记录稀少且亲缘关系不明;3)瓮安生物群中的"单极内移型腔原肠胚"和"分层型腔原肠胚"化石的可靠性尚有待更多的标本提供佐证。瓮安生物群中颇具多样性的原肠胚期动物化石为探索后生动物在晚新元古代的胚胎发育模式开拓了思路。     

湖北宜昌埃迪卡拉系陡山沱组天柱山卵囊胞——Tianzhushania的新认识

我国南方陡山沱组的渗透矿化微体化石为认识埃迪卡拉动物辐射前的生物多样性,提供了异乎寻常的窗口;其中包括一些被视为早期动物胚胎的磷酸盐化球形化石。但是,一些学者将之与现生Thiomargarita sp．比较,把陡山沱组胚胎解释为巨大氧化硫细菌。湖北宜昌晓峰河剖面陡山沱组中发现Tianzhushania的大型具刺疑源类的膜壳中显示有1、2、4、8、16乃至数百个卵裂细胞标本,表明它们应是真核生物,很可能是在滞育卵囊胞中保存的早期卵裂的动物胚胎。此有力地论证了我国南方埃迪卡拉纪陡山沱组动物胚胎化石的保存,并将动物化石记录推前至632Ma前。为了区别Tianzhushania的已知形态种,新建Tianzhushania fissura sp．nov．和Tianzhushania confrerta sp．nov．两个新种,它们分别以含有不同数量卵裂细胞为特征。它们在陡山沱组中、上部的集中保存,可能与海平面变化或其它地质事件密切相关。而这需要更多有效年代地层资料加以合理解释。     

陕西宁强早寒武世磷酸盐化具星状表饰胚胎化石研究

后生动物胚胎化石研究对了解寒武纪大爆发中生命的个体及系统发育具有十分重要的意义。陕南早寒武世灯影组宽川铺段发现大量磷酸盐化的球状化石标本,其中的一些为保存有十分精细的星状表饰的胚胎化石,目前发现至少3种具星状纹饰的胚胎化石:圆球状胚胎、具中央收缩带的球状胚胎和表面具“拉伸构造”的花生状胚胎,其中后者为新类型。研究表明,此新类型在演化序列上处于圆球状胚胎、具中央收缩带的球状胚胎发育阶段之后,是胚胎向成体演化的一个重要中间过渡环节,这一发现为研究早寒武世早期后生动物胚胎及个体发育提供了新线索。     

陕南寒武系底部保存精美的Punctatus胚胎及孵化幼体化石(英文)

在陕南寒武系底部的宽川铺段不仅保存了大量的小壳化石,而且还有诸多后生动物的卵和胚胎化石。目前,大量的胚胎化石已被报道,但是对古老的后生动物早期的个体发育却鲜有报道,尽管Bengtson和Yue(1977)建立了Olivooides的发育序列,但仍缺少一些重要的中间环节,而且胚胎的早期卵裂阶段还不是很清楚。因此,Olivooides和Punctatus之间的联系很难确立。本文报道了宽川铺生物群中新发现的精美的Punctatus的卵裂期、囊胚期及孵化幼体阶段的胚胎化石标本,这些新发现不仅填补了Punctatus发育序列中的空白,而且揭示了Olivooides和Punctatus之间的联系。这些新收集的Punctatus的卵裂期和孵化期的化石特征及Punctatus的形态学证明了Punctatus不是浮游生物,而是底栖生物。大量的胚胎化石和Punctatus的孵化幼体化石标本为我们研究后生动物早期演化提供了线索。     

贵州埃迪卡拉纪瓮安生物群化石含量的统计分析

贵州瓮安埃迪卡拉纪陡山沱组（635-551Ma）上磷矿段保存了大量精美的磷酸盐化微体球粒化石,它们主要由多细胞藻类、疑源类和处于不同发育阶段的多种动物胚胎化石组成,此外还包括少量后生动物的幼、成体化石。本文以贵州瓮福磷矿陡山沱组上磷矿段灰白色球粒状白云质磷块岩为研究对象,在总结瓮安生物群中不同生物化石的鉴别特征基础上,定量统计采自该层位的两组岩石样品（WA—I和WA-r1）的酸处理砂样中的所有化石。统计结果表明,瓮安陡山沱组该磷块岩中化石质量和岩石中磷酸盐组分质量成正线性相关,两个样品中化石占全部磷酸盐组分的质量百分比均在10％左右,其中多细胞藻类和疑源类化石占全部化石含量均少于10％。这一结果客观地反映了瓮安生物群的化石丰度,证实了保存在瓮安陡山沱组上磷矿段灰色富氧含磷埋藏相中的瓮安生物群主要由动物胚胎化石组成的特征。     

我国发现约6亿年前的古老动物 可能为迄今发现的最古老动物

我国古生物学家与美国专家近日对在贵州瓮安发现的胚胎化石研究认为,这个距今约6亿年的动物胚胎化石可能是迄今发现的最古老动物。     

动物的起源和寒武纪大爆发:来自中国的化石证据

近30年来,中国埃迪卡拉纪—寒武纪发现了包括瓮安生物群和澄江动物群在内一系列重要化石群,为揭示动物的起源和寒武纪大爆发过程提供了全球独一无二的古生物学证据。文中全面而简洁地介绍发现于华南埃迪卡拉纪—寒武纪的所有化石群和重要动物化石发现,总结其中特异化石群保存类型和埋藏环境。其中,陡山沱型磷酸盐化胚胎化石群、庙河型宏体碳质膜化石群和牛蹄塘型海绵动物群,以及陡山沱组硅化的动物休眠胚胎化石和宽川铺动物群中"rsten"型化石均是全球这一时期华南独有的特异埋藏化石群。从时空两方面对化石群进行综合分析认为,动物可靠的最早化石记录发现于埃迪卡拉纪早期,成冰纪及其以前的动物化石均存在疑问。动物的起源和寒武纪大爆发经历了从浅水逐步向深水迁移,以及阶段性辐射和灭绝的过程。首先动物经历了在埃迪卡拉纪早期的隐形微体动物早期演化阶段,之后经过以埃迪卡拉型生物为代表的大型复杂化演化阶段,在寒武纪初期发生以梅树村动物群为代表的两侧对称动物和生物骨骼矿化的大爆发,并随后又被以澄江动物群为代表的寒武纪动物群所替代,在筇竹寺期达到了动物造型和生态系统复杂化的高峰。     

动物的起源和寒武纪大爆发：来自中国的化石证据北大核心

近30年来,中国埃迪卡拉纪—寒武纪发现了包括瓮安生物群和澄江动物群在内一系列重要化石群,为揭示动物的起源和寒武纪大爆发过程提供了全球独一无二的古生物学证据。文中全面而简洁地介绍发现于华南埃迪卡拉纪—寒武纪的所有化石群和重要动物化石发现,总结其中特异化石群保存类型和埋藏环境。其中,陡山沱型磷酸盐化胚胎化石群、庙河型宏体碳质膜化石群和牛蹄塘型海绵动物群,以及陡山沱组硅化的动物休眠胚胎化石和宽川铺动物群中"rsten"型化石均是全球这一时期华南独有的特异埋藏化石群。从时空两方面对化石群进行综合分析认为,动物可靠的最早化石记录发现于埃迪卡拉纪早期,成冰纪及其以前的动物化石均存在疑问。动物的起源和寒武纪大爆发经历了从浅水逐步向深水迁移,以及阶段性辐射和灭绝的过程。首先动物经历了在埃迪卡拉纪早期的隐形微体动物早期演化阶段,之后经过以埃迪卡拉型生物为代表的大型复杂化演化阶段,在寒武纪初期发生以梅树村动物群为代表的两侧对称动物和生物骨骼矿化的大爆发,并随后又被以澄江动物群为代表的寒武纪动物群所替代,在筇竹寺期达到了动物造型和生态系统复杂化的高峰。     

Exogenous peroxidase in the eggs of rats during cleavage]

The presence of exogenous peroxidase of the rat's eggs during cleavage at the 1-, 2-, 8-cellular stages and the blastocysts were studied after 30 minute incubation with horseradish peroxidase (molecular weight 40.000, approximate size of the molecule 40 A). The activity of exogenous peroxidase in the area of zona pellucida was established in the perivitelline space, in the cytoplasm - in the pinocytosis vesicles, in certain greater vacuoles and in certain secondary lysosomes. At the stage of blastocyst the penetration of exogenous protein was greater than at earlier stages. The reaction product was found here in the intercellular space and in the blastocyst cavity. The obtained data suggest possible penetration of the protein from the surrounding area into the egg during its passing the uterine tube. The substances influencing the differentiation of the egg or teratogens may penetrate the egg in the same way.     

Structure, localization and potential role of a novel molluscan trypsin inhibitor in Lymnaea.

Eggs and egg masses of the freshwater gastropod mollusc Lymnaea provide a microenvironment for developing embryos. Secretions of the exocrine albumen gland of Lymnaea are packaged in the eggs of an egg mass before the eggs are laid externally. The perivitelline fluid that directly surrounds individual oocytes is the main source of nutrition for developing embryos. During early stages of development, the perivitelline fluid is initially internalized by pinocytosis and degraded by lysosomes; in later stages, the embryo ingests the fluid. We previously found that the albumen gland produces large amounts of Lymnaea epidermal growth factor. The albumen gland also appears to produce significant amounts of a novel Lymnaea trypsin inhibitor (LTI), a second peptide that was purified and characterized from Lymnaea albumen gland extracts. The primary structure was determined by microsequence analysis, mass spectrometry, and C-terminal sequence analysis, and showed that LTI is a 57-residue glycosylated peptide. Comparison of the LTI sequence with other known serine protease inhibitors indicates that LTI is a member of the bovine pancreatic trypsin inhibitor family. Reverse phase-high performance liquid chromatography, microsequence analysis, mass spectrometry, and immunocytochemistry demonstrated that abundant amounts of intact LTI are packaged in egg masses. The presence of a trypsin inhibitor in the perivitelline fluid compartment of the egg mass may minimize digestion of peptides and proteins in the perivitelline fluid that are important for the development of the embryo, for example, Lymnaea epidermal growth factor.     

Establishment of self-sterility of eggs in the ovary of the solitary ascidian,Halocynthia roretzi

When unfertilized eggs (UFE) of the solitary ascidian, Halocynthia roretzi, are released naturally they are strictly self-sterile, whereas almost all ovarian eggs isolated after spawning are self-fertile. Self-sterile eggs are prepared within a relatively short period of several hours before the spawning. The morphological changes in ovarian eggs during late oogenesis were studied with special reference to the establishment of self-sterility. Four types of eggs at serial developmental stages were classified according to the morphology of their external envelopes. Self-sterility was established in the last stage, from the ovarian egg type 3 (OVE3) to UFE stages. Ovarian eggs which had become committed to UFE were denoted as full-grown ovarian eggs (FOE). FOE were able to differentiate into self-sterile UFE in vitro, whereas OVE3 could not. Several morphological differences between OVE3 and UFE were found. OVE3 had a germinal vesicle (GV), a type of vitelline coat (VC-OVE3) and no expanded perivitelline space, whereas UFE had completed germinal vesicle break down (GVBD), had another type of coat (VC-UFE) and showed an expanded perivitelline space. There were also some differences in the mode of fertilization between OVE3 and UFE. In UFE, sperm became bound firmly to the vitelline coat and passed through the coat with the help of follicle cells, whereas in OVE3, sperm did not bind so strongly and entered the perivitelline space without the aid of follicle cells. The relationships between the establishment of self-sterility and these morphological and functional changes in ovarian eggs are discussed.     

FORMATION OF THE CORTICAL CONCAVITY AT FERTILIZATION IN THE SEA URCHIN EGG

During the initial stages of fertilization envelope elevation in eggs of Strongylocentrotus pur puratus and S. droebachiensis a large concavity of the egg cortex was observed in the light microscope. This concavity corresponded in shape and size with the elevating fertilization envelope. However, after the vitelline layers of eggs were disrupted and the eggs inseminated, the concavity failed to develop although the eggs were fertilized and developed normally. We propose that the concavity is formed owing to increased hydrostatic pressure within the perivitelline space. To further support this hypothesis we measured total egg protein secreted during fertilization, and found that 98% was retained within the perivitelline space. Furthermore, 80% of the total protein was contributed by the hyaline layer. Presumably, colloidal osmotic pressure and/or hydration of fertilization product, trapped beneath the fertilization envelope, is responsible for increased hydrostatic pressure within the perivitelline space, and therefore promotes not only fertilization envelope elevation, but the cortical concavity as well.     

Cleavage Events and Sperm Dynamics in Chick Intrauterine Embryos

This study was undertaken to elucidate detailed event of early embryogenesis in chicken embryos using a noninvasive egg retrieval technique before oviposition. White Leghorn intrauterine eggs were retrieved from 95 cyclic hens aged up to 54-56 weeks and morphogenetic observation was made under both bright field and fluorescent image in a time course manner. Differing from mammals, asymmetric cleavage to yield preblastodermal cells was observed throughout early embryogenesis. The first two divisions occurred synchronously and four polarized preblastodermal cells resulted after cruciform cleavage. Then, asynchronous cleavage continued in a radial manner and overall cell size in the initial cleavage region was smaller than that in the distal area. Numerous sperms were visible, regardless of zygotic nuclei formation. Condensed sperm heads were present mainly in the perivitelline space and cytoplasm, and rarely in the yolk region, while decondensed sperm heads were only visible in the yolk. In conclusion, apparent differences in sperm dynamics and early cleavage events compared with mammalian embryos were detected in chick embryo development, which demonstrated polarized cleavage with penetrating supernumerary sperm into multiple regions.     

An ultrastructural study of epididymal mouse spermatozoa binding to zonae pellucidae in vitro: sequential relationship to the acrosome reaction

Mouse sperm bind to the zona pellucida of the egg prior to penetration of the zona and entry into the perivitelline space. The question then arises: when does the acrosome reaction occur relative to these processes? An ultrastructural study of mouse epididymal sperm bound to the surface of the zona and in the privitelline space was undertaken to clarify this point. Cumulus-free mouse eggs were inseminated in either a complete defined culture medium capable of supporting in vitro fertilization or in Tris/NaCl buffer containing Ca+2. Both media support sperm binding to the zona to the same extent; binding is complete in 15 minutes. Unbound sperm were removed by a step gradient density centrifugation to yield a preparation of eggs with sperm firmly bound. All sperm in the perivitelline space had undergone the acrosome reaction. Sperm bound at the surface of the zonae pellucidae of eggs recovered at ten minutes after insemination all had intact acrosomes. At 40 minutes after insemination, half of the sperm were intact; the other half were in the initial stages of the acrosome reaction. At 90 minutes after insemination, 12% of the sperm had undergone the full acrosome reaction and were starting to penetrate the zona; of the balance, half were in various stages of the acrosome reaction, while half were still intact. These findings support the hypothesis that the sequence of the early reactions leading to fertilization in the mouse is: intact sperm binding to zona; acrosome reaction at the zona surface; penetration of the zona.     

The swelling egg of the long rough dab, Hippoglossoides platessoides limandoides (Bloch)

The egg of Hippoglossoides platessoides limandoides swells when released into sea water. The swelling takes place entirely outside the ovoplasm and creates a large perivitelline space which can make up 85% of the total egg volume. Swelling occurs in both unfertilized and fertilized eggs although a small proportion of unfertilized eggs, believed not to have been activated, do not swell. Swelling is dependent upon the breakdown of cortical alveoli, together with an unusually soft and elastic chorion. The cortical alveoli, present in greater numbers than is usual in teleost eggs, release colloidal material when they break down on egg activation; adsorption of water by this material is responsible for the egg volume increase.     

Deterioration patterns in diapausing egg banks of Brachionus (Müller, 1786) rotifer species

Rotifers are cyclical parthenogens that produce sexual diapausing eggs at some stage in their life cycle. These eggs are encysted embryos that remain viable for extended periods in lake and pond sediments, thus acting as an egg bank with many ecological and evolutionary consequences. Despite its importance to rotifer evolution, there are no studies on resting egg deterioration and associated processes in natural environments. In this study, more than 4000 diapausing eggs of species from the Brachionus plicatilis complex, which includes several closely related cryptic species, were collected from different sediment depths in 15 ponds in eastern Spain and were classified according to three features thought to be related to their viability: shell integrity, embryo size, and embryo colour. A positive association was found between embryo size and hatching success in those eggs having an intact shell. Diapausing eggs that showed good shell integrity and no more than a 25% reduction of multinuclear embryo maximum size were classified as healthy and 98.9% hatched. Darkening of diapausing egg embryo was an indicator of viability loss. A decreasing frequency of healthy-looking diapausing eggs was observed with increasing sediment depth, although some exceptions were found.     

Development of eggs and larvae of Stolephorus commersonnii and taxonomic key to fish eggs of the Clupeidae and Engraulidae off China

Fish eggs of successive stages of embryonic development, which were identified as belonging to specimens of Commerson's anchovy Stolephorus commersonnii through comparative molecular techniques, were collected from Leqing Bay, Zhejiang, China. Some eggs were reared artificially to obtain samples of successive developmental stages of larvae. The fertilized eggs of S. commersonnii are ellipsoidal and non-adhesive. The surface of the egg membrane is smooth and the perivitelline space is narrow. There is a single oil globule in the irregularly segmented yolk. Newly hatched larvae are transparent and devoid of pigments. Development of the larvae occurs in the following sequence: 8?h after hatching, the anus unfolds; 12?h after hatching, the pectoral fins emerge; 24?h after hatching, the liver and branchial arches emerge, and the alimentary canal differentiates into the oesophagus and intestinal canal; 30?h after hatching, the eyes become pigmented; 36?h after hatching, the upper and lower jaws become distinct; 42?h after hatching, the stellate melanophores emerge; 72?h after hatching, the postlarval developmental stage begins with the emergence of the dorsal fin. Based on the morphology of eggs and larvae of S. commersonnii, a taxonomic key to fish eggs of the Clupeidae and Engraulidae off China is established to provide an efficient and convenient way to identify the egg specimens. The fish eggs of the Clupeidae and Engraulidae off China could be identified to some extent by the buoyancy, shape and diameter of eggs, the number of layers in the egg membrane, the size of the perivitelline space, the number and diameters of oil globules, and the distribution of pigments. Meanwhile, their prelarvae could be identified by the number and diameters of oil globules, the distribution of pigments, the location of the anus and the number of myomeres.     

Adaptive value of the volume of perivitelline fluid in the eggs of euphausiids (Crustacea: Euphausiacea)

The perivitelline space of the euphausiid egg serves to maintain eggs buoyancy. It is believed that in oceanic species the volume of the perivitelline space is smaller than in neritic [32, 37, 40]. Published and original data suggest a more complicated tendency for perivitelline space volume and, correspondingly, egg buoyancy in euphausiids, which decrease in the direction: continental slope → shelf → ocean. This tendency is well explicable by adaptations of euphausiid species to the specific conditions of these biotopes. The possible mechanisms of these adaptations are discussed.