志留纪笔石Oktavitesexcentricus(Bjerreskov,1975)的古生物学特征及地层意义*

陕西紫阳地区在古地理上位于扬子台地西北缘,区域内志留纪地层发育,其中志留系兰多维列统(Llandovery)特列奇阶(Telychian)笔石相地层出露较为完整,笔石带较为连续。Oktavites excentricus(Bjerreskov,1975)是特列奇阶Oktavites spiralis笔石带重要的伴生分子,在世界范围内广泛分布。文中通过对紫阳地区一系列特列奇阶剖面研究后认为,Oktavites excentricus较短的化石延限和广泛的古地理分布使其具备地层对比潜力,这将为Oktavites spiralis笔石带的进一步细分提供依据。同时,Oktavites excentricus胞管为典型的奥氏笔石式,其笔石体的盘旋方式又与稍晚的Cyrtograptus lapworthi(Tullberg,1883)(笔石带化石,弓笔石类的早期代表)十分接近,因此,对该种的演化过程的研究也为讨论弓笔石的起源过程提供了更多参考。     

黔北石阡雷家屯志留系埃隆阶-特列奇阶界线附近几种胞石之记述*

一、前言特列奇阶作为一个阶,国际地层委员会业已批准下列界定:以turriculatus带之底作下界,以crenulata之顶作上界(Holland,1985)。在以笔石占绝对优势的斜坡相区,如陕南紫阳地区,界定特列奇阶并无困难(傅力浦、宋礼生,1986)。而在以介壳相为主的陆棚相区,尤其在内陆棚相区,如何界定特列奇阶确非易事。林宝玉等(1982)所定义的石牛栏阶即是一例。石牛栏阶的命名地点和层型剖面在四川綦江观音桥。按照他们的意见,石牛栏阶的下界“大致相当于笔石相的Spirograptus turriculatus带”(林宝玉等,1982,145页)。由于并无可靠的、足以确证属于Spirograptus turriculatus带的笔石作为依据,这一结论似乎虚悬无着。     

黔北石阡雷家屯志留系埃隆阶-特列奇阶界线附近几种胞石之记述

一、前言特列奇阶作为一个阶,国际地层委员会业已批准下列界定:以turriculatus带之底作下界,以crenulata之顶作上界(Holland,1985)。在以笔石占绝对优势的斜坡相区,如陕南紫阳地区,界定特列奇阶并无困难(傅力浦、宋礼生,1986)。而在以介壳相为主的陆棚相区,尤其在内陆棚相区,如何界定特列奇阶确非易事。林宝玉等(1982)所定义的石牛栏阶即是一例。石牛栏阶的命名地点和层型剖面在四川綦江观音桥。按照他们的意见,石牛栏阶的下界“大致相当于笔石相的Spirograptus turriculatus带”(林宝玉等,1982,145页)。由于并无可靠的、足以确证属于Spirograptus turriculatus带的笔石作为依据,这一结论似乎虚悬无着。也     

华南特马豆克期笔石地层分带及全球对比

特马豆克阶是奥陶系底部第一个阶,笔石是特马豆克阶高分辨率地层划分与对比的重要化石类群。江南斜坡带是我国早奥陶世特马豆克期漂浮笔石分异度和丰度最高的相区之一,位于该区的湖南益阳南坝剖面,发育有完整的上特马豆克阶笔石地层,特马豆克阶-弗洛阶界线附近地层连续,上特马豆克阶笔石地层研究已取得较大进展,但下特马豆克阶地层缺乏系统研究。近年来,通过对该剖面笔石标本的不间断采集,新识别出下特马豆克阶笔石带Rhabdinopora flabelliformis parabola带。到目前为止,湖南益阳南坝剖面特马豆克阶可以识别出5个笔石带,自下而上依次为:Rhabdinopora flabelliformis parabola带、Adelograptus tenellus带、Aorograptus victoriae带、Araneograptus murrayi带以及Hunnegraptus copiosus带。基于目前已识别出的笔石带,参考国内外同期笔石地层资料,本文详细讨论华南特马豆克期笔石带序列,并与国内外同期地层进行精确对比。     

奥陶-志留系界线地层生物带的全球对比

详述扬子区晚奥陶世晚期(阿什极期)至兰多维列世初期的生物带序列,修正部分的笔石带,与全球各重要地区进行对比.研究表明,全球奥陶系顶部赫南特亚阶及其上下地层在我国的扬子区发育最好,地层连续发育并广泛出露,生物带发育齐全,不但有连续的笔石带,而且有世界广布的赫南特贝腕足动物群,有望在我国建立赫南特亚阶的全球层型剖面和点(GSSP).     

扬子区志留纪兰多维列统胞石序列

扬子区志留系的兰多维列统(Llandovery),以笔石最丰,研究亦最详.正是已故的穆恩之教授,"奠定了我国笔石地层的分层和笔石分带的基础"(卢衍豪,1987,14页).然而,有些地层不仅不含笔石,而且其它大化石,或缺如,或偶有见及,亦难作洲际对比.因此,这些地层的时代问题纷争不已.又是穆师高瞻远瞩,生前多次疾呼,要研究微体化石并对其寄予厚望.作者对于兰多维列统胞石序列的研究,正是在他的大力支持与亲切关怀下开展起来的.如今,在这些地层中已相继觅得有助于确定时代的胞石类化石.胞石序列,草创初成,始可告慰穆师于九泉之下.     

奥陶—志留系界线地层生物全球对比

详述扬子区晚奥陶世晚期（阿什极期）至兰多维列世初期的生物带序列,修正部分的笔石带,与全球各重要地区进行对比,研究表明,全球奥陶系顶部赫南特亚阶及其上下地层在我国的扬子区发育最好,地层连续发展育并广泛出露,生物带发育齐全,不但有连续的笔石带,而且有世界广布的赫南特贝腕足动物群,有望在我国建立赫南特亚阶的全球层型剖面和点（ＧＳＳＰ）。     

尖笔石类的发育型式及其系统分类位置

一前言尖笔石类的笔石在亚洲、欧洲及北美洲早志留世地层中分布广泛。由于这类笔石层位稳定,一直当作下志留统重要的标准化石,并用来建立笔石带,进行地区间及世界范围的对比。虽然自1867年就开始对这类笔石进行研究,但直到目前,对这类笔石的始端性质及发育型式,还没有完全搞清楚,因而对其系统分类位置的认识一直未能得到令人满意的结果。这对于进一步研究此类笔石的发生、演化及其系统分类     

Ningxiagraptus的再研究

甘肃平凉的平凉组和新疆柯坪大湾沟的萨尔干组中具有大量保存良好的Ningxiagraptus(宁夏笔石属)标本,为其研究提供了极佳的化石材料。本文结合新发现的材料,对Ningxiagraptus的分类位置进行厘定,对其变革历史中存在的若干问题进行讨论,为深入研究笔石的分类提供一个可供参考的案例。在对正笔石目笔石的分类和亲缘关系判别时,以笔石体的始端发育型式和特征为主,辅以笔石枝的结合方式及胞管性质是可行的方法。Ningxiagraptus虽具简单直管状胞管,第2个胞管自胎管口部向上转曲伸出,构成"U"字形始端,但其始端发育型式和始端形态却与Dicellograptus(叉笔石)近似,故将Ningxiagraptus归属有轴亚目的双头笔石超科。     

吉林大阳岔剖面奥陶纪最早期笔石的再研究

对吉林白山大阳岔剖面奥陶纪最早期的笔石进行了再研究,论述了Ｒｈａｂｄｉｎｏｐｏｒａ属的始部发育型式,认为该属只限于４个原始笔石枝组成的笔石;从笔石体外形、笔石枝特征横杷能网眼、曲折度和线管构造等方面,对大阳岔剖面Ｒｈａｂｄｉｎｏｐｏｒａ ｆｌａｂｅｌｌｉｆｏｒｍｉｓ ｐａｒａｂｏｌａ居群的形态变异作了详细研究,地正确论战该种特征和进行系统分类研究具有重要作用。重新描述了太阳岔剖面奥陶纪最早期的笔石     

Characteristics of the membranes of the pellicle of the ciliatePseudomicrothorax dubius

Summary The membranes of the pellicle of the ciliatePseudomicrothorax dubius are investigated using thin section electron microscopy and freeze-fracture replicas. The plasma membrane is covered by a surface coat and is connected to the outer alveolar membrane by short, sometimes branched, bridges. The inner alveolar membrane is coated on both sides. The epiplasm lies in intimate contact with the cytoplasmic surface of this membrane, and there is a corresponding deposit on the other surface. This deposit is regularly striated.The epiplasmic layer and the alveoli are interrupted at sites of cytotic activity,e.g., the attachment sites of trichocysts, the cytoproct, and the parasomal sacs. The striated deposit ends where the epiplasm ends, indicating a direct relationship between these two epimembranous layers.There is a deposit along the sides of the first part of the tip of the trichocysts, and in this region the trichocyst membrane is free of intramembranous particles.The membrane of the parasomal sacs has a coat on both surfaces. That on the extraplasmic surface is similar to the surface coat of the plasma membrane. The origin of the cytoplasmic coat is unknown. The cytotic activity of these sacs is indicated by their highly irregular profiles.     

The early development of the tail and the transformation of the shape of the nucleus of the spermatid of the domestic fowl,Gallus gallus

Summary The differentiation of the spermatid, especially in reference to the formation of the flagellum, and transformation of the shape of the nucleus was investigated in the domestic fowl.In the early stage of the spermatid, a prominent Golgi apparatus appears around the centrioles. The Golgi vesicles then surround the axial-filament complex which develops from the distal centriole. These vesicles fuse to form continuous membrane at the earliest stage of flagellar formation, and in the succeeding stage Golgi lamellae are attached to the plasma membrane of the developing flagellum. From these observations, it is assumed that Golgi apparatus may be a source of the membrane system of the flagellum.The microtubules distributed around the nucleus form the circular manchette. The anterior region of the nucleus with the manchette is cylindrical in shape and the posterior region without it remains irregular in shape. When the circular manchette has been completed, the whole nucleus acquires a slender cylindrical shape. The circular manchette then changes into the longitudinal manchette. The nuclei of spermatids without a longitudinal manchette are abnormal in shape. In view of these observations it is assumed that the nuclear shaping of the spermatid may be accomplished by circular manchette and the maintenance of shape of the elongated nucleus by longitudinal manchette.The authors wish to thank Mr. Takayuki Mori for his helpful suggestions and technical advices     

Separation of the pineal vesicle from the wall of the third ventricle during the post-hatching development of the chicken

Summary According to light- and electron-microscopic observations the pineal organ of the 3-day-old chicken consists of a prominent end vesicle and a tapering parenchymal stalk. During this stage the pineal lumen is in open communication with the third ventricle. However, in the 40-day-old chicken, which still possesses a well-developed end vesicle, the proximal portion of the pineal stalk displays regressive changes leading to local fragmentation. At this stage the pineal stalk is reduced, and the pineal lumen is missing. In 1-year-old chickens the parenchyma of the proximal portion of the stalk is further diminished, and in 3-year-old domestic fowl is completely displaced by bundles of collagenous fibers, only some nerve fibers being present. This post-hatching pineal development may reflect the sequence of changes leading from pineal sense organs to pineal glands.This work was supported by a grant-in-aid for Scientific Research from the Ministry of Education, Science and Culture of Japan