Microstructural organization of the central nervous system in the harvestman Leiobunum japonicum (Arachnida: Opiliones)

Although the order Opiliones constitutes the third‐largest group of arachnids, this creature is still mysterious and has a rich unexplored field compared to what is known about insects and crustaceans. The order Opiliones is traditionally regarded as a close relative of mites, mainly because of morphological similarities in external body structure; however microstructural organization of the ganglionic neurons and nerves in the harvestman Leiobunum japonicum is quite similar to the central nervous system (CNS) in all extant arachnids. The CNS consists of a large neural cluster with paired appendicular nerves. The esophagus passes through the neural cluster and divides it into the upper supraesophageal ganglion (SpG) and the lower subesophageal ganglion (SbG). The dorsal part of the SpG has a quite condensed cell body compared with other parts of the CNS and has two main components, the protocerebrum and the cheliceral ganglion. The protocerebrum receives the optic nerves and has four main groups of neuropiles from the optic lobes, the superior central body, the lateral neuropils (corpora pedunculata) and the inferior neuropil. However, a pair of pedipalpal and four pairs of appendage nerves including several pairs of abdominal nerves arise from the nerve masses of the SbG.     

Nanoporous Structures Similar to Those Reported from Squid Sucker Teeth are also Present in Egg Shells of a Terrestrial Flatworm (Platyhelminthes; Rhabditophora; Geoplanidae) from Hachijojima (Izu Islands,Japan)

Shells of the egg cocoon of a terrestrial planarian (Diversibipalium sp.) from Hachijojima were found to be composed of a lattice of parallel nanotubes of ca. 120 nm diameter oriented perpendicular to the shell's surface. The arrangement of the porous proteinaceous tubes closely resembles that has recently been reported from the sucker teeth of squid and to date is the only other example of this kind of structure. Although the array of nanotubes undoubtedly contributes to the stiffness of the shell and helps protecting the embryo, questions such as to how the planary worm produces the array of nanotubes and what exactly their chemical and physical properties are versus those of the squid sucker tooth still remain to be answered.     

The problem of Dinosaur extinction.Contribution of the study of terminal Cretaceous eggshells from Southeast France

A biostratigraphic sequence based upon dinosaureggshells during the lower and upper Rognacian (upper Cretaceous) in the Aix-en-Provence sedimentary basin (Bouches-du-Rhône, France) has been studied from a morphometric and microstructural viewpoint. Stratigraphic control of eggshell fragment sampling made it possible to follow their evolution throughout the Rognacian. Our results differ from those of certain authors who have worked in this region in that no tendancy toward abnormal eggshell thinness appears at the end of the Cretaceous which could be linked to the problem of dinosaur extinction. Furthermore, we observed no significant increase in the number of bi- or multistratified eggshells («ovum-in-ovo) in the deposits. The microstructural study shows the presence mainly of normal egg-shells belonging to at least three morphotypes.     

北方山溪鲵精子发生不同阶段的显微与超微结构

用光镜和电镜观察了北方山溪鲵(Batrachuperus tibetanus)精子发生过程中各种类型生精细胞的显微与超微结构变化。结果显示,北方山溪鲵在4~8月时处于精子发生期,精子形成在7~8月。成熟精子的结构具有小鲵科精子的一些共同特征,如顶体前端呈三叶草状,尾部由轴纤维、波动膜、轴丝及轴丝旁纤维构成,轴纤维粗大呈圆柱形,尾部无线粒体等。比较分析认为,在两栖类的系统发育中,轴纤维、波动膜和轴丝旁纤维的消失为近裔性状。     

Age-related properties at the microscale affect crack propagation in cortical bone

The increased risk for fracture with age is associated not only with reduced bone mass but also with impaired bone quality. At the microscale, bone quality is related to porosity, microstructural organization, accumulated microdamage and intrinsic material properties. However, the link between these characteristics and fracture behavior is still missing. Bone tissue has a complex structure and as age-related compositional and structural changes occur at all hierarchical length scales it is difficult to experimentally identify and discriminate the effect of each mechanism. The aim of this study was therefore to use computational models to analyze how microscale characteristics in terms of porosity, intrinsic toughness properties and microstructural organization affect the mechanical behavior of cortical bone. Tensile tests were simulated using realistic microstructural geometries based on microscopy images of human cortical bone. Crack propagation was modelled using the extended finite element method where cement lines surrounding osteons were modelled with an interface damage law to capture crack deflections along osteon boundaries. Both increased porosity and impaired material integrity resulted in straighter crack paths with cracks penetrating osteons, similar to what is seen experimentally for old cortical bone. However, only the latter predicted a more brittle failure behavior. Furthermore, the local porosity influenced the crack path more than the macroscopic porosity. In conclusion, age-related changes in cortical bone affect the crack path and the mechanical response. However, increased porosity alone was not driving damage in old bone, but instead impaired tissue integrity was required to capture brittle failure in aging bone.     

Modeling the Rheological Properties of Fats: A Perspective and Recent Advances

The elastic modulus of colloidal fat crystal networks scales with the volume fraction of solids in a power–law fashion. To explain and predict how the elastic properties of these networks change with their volume fraction of solids, several physical models have been proposed. In this review, the chronology of the development of structural–mechanical models to explain the elasticity of fats is reviewed, leading to the development of the fractal model. In the fractal model, the fractal-like behavior of fat crystal networks, which can be considered fractal gels of polycrystals in oil, or colloidal crystals, is used to explain the power–law scaling behavior of the shear elastic modulus to the volume fraction of solids. Lately, however, many experimental results and simulation studies suggest that the stress distribution within networks can be dramatically heterogeneous, which means that a small part of the network carries most of the stress. This concept was introduced into a modified fractal model by deriving an expression for the effective volume fraction of stress-carrying solids. The modified fractal model fits the experimental data well and successfully explains the sometimes observed non-linear log–log behavior between the shear elastic modulus and the volume fraction of solids.     

久效磷对美国红鱼鳃Na^＋／K^＋-ATP酶活性和超显微结构的影响

经不同试验浓度的久效磷(0．25、0．5、1．0和2．0mg·L^-1)处理美国红鱼4d后,分别对鱼鳃Na^+／K^+—ATP酶活性和氯细胞密度进行了测定和计数,并观察了鱼鳃组织显微结构和超微结构的变化。结果表明,低浓度久效磷(0．25mg·L^-1)处理可以诱导鱼鳃氯细胞大量增生,Na^+／K^+—ATP酶活性增强,随着试验浓度的增加,久效磷对鳃组织的损伤越来越重,Na^+／K^+—ATP酶活性逐渐降低;久效磷对鱼鳃显微结构的损伤表现为鳃小片上皮细胞水肿、脱离。鳃小片基部粘连。鳃小片上皮细胞角质化;超微结构变化主要为内质网、线粒体、微小管和核膜的水肿及部分溶解,这种损伤表现为由细胞膜到细胞核的动态过程。     

中华稻蝗受精囊的显微与超微结构

在显微及亚显微水平上研究了中华稻蝗受精囊的结构。该结构由外向内依次为：围脏膜,肌肉层,结缔组织,基膜,上皮层和内膜层。其中内膜层又分为上表皮,外表皮和内表皮三层,其间可见许多分泌小管。上皮层分别由锥形分泌细胞和长柱形细胞组成,前者内含大量的分泌泡。肌肉层由环肌和纵肌构成,其中环肌比较发达。     

Hyolith-type microstructure in a mollusc-like fossil from the Early Cambrian of Yunnan, China

A phosphatized bilaterally symmetrical, spirally coiled conch from the Lower Cambrian phosphates of the Meishucunian Stage of eastern Yunnan, China, is composed of two well-preserved layers. The outer one is built of longitudinal mineralized fibres not strictly parallel to each other, but may anastomose or branch. The fibres form comarginal ribs with transversal grooves between them, corresponding to growth stages. In the ribs, the fibres are arranged closely and are steeply inclined towards the apex, while in the grooves the fibres are subparallel to the conch surface and more loosely packed. Small elliptic and triangular holes are situated within and between the fibres of the outer layer. The inner layer consists of transversal fibres running around the conch. They are almost parallel to each other but partly separated by narrow discontinuous slits. Despite overall morphological similarity of the conch to shells of some early Cambrian molluscs, the observed orthogonal configuration of longitudinally oriented fibrous structures of the outer layer and transversal fibres of the inner layer is found in orthothecid hyoliths, phosphatized microstuctures of which have been described from the Lower Cambrian of the Siberian Platform. The new material from the Yangtze Platform supports a conclusion of a distinctive type of microstructure available in hyoliths different from molluscan microstructures available from the Lower Cambrian.     

两种圆柏属植物不同季节显微和超微结构变化与耐寒性的关系

以祁连圆柏和圆柏为材料,研究了圆柏属植物的抗寒性与解剖结构变化,以及淀粉与可溶性糖粉转化的关系.结果表明,祁连圆柏和圆柏叶片的上下表皮细胞外覆盖一层角质膜,叶肉细胞间隙大,形成发达的通气组织.在生长季节,二者叶绿体内均积累了很多淀粉粒,在冷冻休眠季节淀粉粒消失或变小,同时叶片可溶性糖分含量增加,祁连圆柏的可溶性糖分增幅高于圆柏;而休眠季节圆柏叶绿体受到低温伤害,脂质球数目增多,出现脂质小滴,部分叶绿体变形,祁连圆柏类囊体的结构受到影响较小,脂质球数量少,叶绿体形状没有发生明显的变化.因此,祁连圆柏和圆柏抗寒性与发达的通气组织和淀粉粒生长季节的积累有关,在低温胁迫下祁连圆柏叶绿体表现出高的稳定性,通过可溶性糖分的调节力强,耐寒性增强.