Feeding Mechanisms and Comparative Functional Morphology of Macrothricidae (Crustacea : Cladocera)

Feeding of the Macrothricidae is accomplished b y two principal methods: active collection of food from the substrate surface and filtration of suspended particles. As differentiated from Ilyocryptus sordidus and Lathonura rectirostris, Ophryoxus gracilis is equipped with the most universal set of limbs allowing catching of food along with filtratory feeding. They are described in detail. Lathonura rectirostris is a highly specialized species, an inhabitant of plant thickets, since i t adapted to feeding on epiphytic algae and particles at the plant surface. Feeding is accomplished only by scraping or catching food by means of complexes of setae of the II pair of limbs. Filtratory feeding and appropriate structures are lacking. The structure and action of the limb apparatus of Ilyocryptus sordidus rule out active catching of food particles.     

Functional Morphology of the Heart in Fishes

The systemic heart of fishes consists of four chambers in series,the sinus venosus, atrium, ventricle, and conus or bulbus. Valvesbetween the chambers and contraction of all chambers exceptthe bulbus maintain a unidirectional blood flow through theheart. The heart is composed of typical vertebrate cardiac muscle,although there may be minor differences in the distributionof spontaneously active cells, the rate and nature of spreadof excitatory waves, and the characteristics of resting andaction potentials between different fish and other vertebrates.Cholinergic fibers innervate the heart, except in hagfish whichhave aneural hearts. Fish hearts lack sympathetic innervation.The level of vagal tone varies considerably, and is affectedby many factors. In some fish the heart is essentially aneural(without vagal tone) during exercise and may resemble an isolatedmammalian ventricle with increased venous return causing increasedcardiac output. There are many mechanisms that could increasevenous return in exercising fish. rß-adrenergic receptorshave been located on the hearts of some fish, and changing levelsof catecholamines may play a role in regulating cardiac activity.Changes in cardiac output in fish are normally associated withlarge changes in stroke volume and small cha-nges in heart rate.     

Functional Morphology of the Teleost Pituitary Gland

The current state of our knowledge of the morphology and histo-and cytophysiology of the teleost pituitary gland is presented.The zonation that characterizes the adenohypophysis is basedon the regional distribution of specific cell types. As a resultthere is also a functional zonation indicated by specific hormonesemanating from clearly identifiable parts of the gland. Theseobservations make the teleost hypophysis ideal for the studyof problems that may be basic to all vertebrates. The ultrastructure of hypophysial cells is presented and relatedto observations at the light microscope level. The manner inwhich secretory granules are released from specific cells iscompared, and the problem of evaluating "cell activity" discussed. The application of immunohistochemical techniques to the studyof the teleost pituitary gland is reviewed, and its use as atool of investigation for future studies evaluated. These methodshave helped to elucidate the cellular source of teleost pituitaryhormones and have confirmed the findings of the histophysiologists.     

Functional Morphology of Mammalian Mastication

SYNOPSIS. While chewing is not unique to mammals, it is oneof their most distinctive characteristics. Historically, studiesof food processing in mammals were intended to provide evolutionaryinsights, but more progress has been made in understanding mechanisticaspects. Mastication is considered under five headings. (1)Interaction of teeth with food.Knowledge of comparative dentalanatomy and function is advanced in comparison to understandingof foods and how they are broken down. (2) Chewing force andits resistance by the skull. The traditional assumption thatocclusal force is maximized is not always justified, and experimentalresults suggest that skull loading is far more dynamic and variablethan had been envisioned from theoretical analyses. (3) Howthe jaw moves. The most important masticatory movement is thatof the power stroke, and in most but not all species this isinfluenced more by the inclined planes of the teeth and jawjoints than by the musculature. (4) The role of muscles in producingboth force and movement. The most fundamental distinction amongjaw muscles is whether they have a rostral or caudal directionof pull, as this determines their role in transverse jaw movements.Reliance on anatomical names tends to obscure functional similaritiesand differences among species. (5) Intraoral structures. Becausethey are difficult to study, the actions of the tongue and pharynxare still debated. Even the fundamental question of whethermammals can breathe and swallow at the same time has not beendefinitively answered.     

Functional Morphology of Stylophoran Echinoderms

The life orientation and mode of life of stylophorans are a subject of much ongoing debate. Examination of the ornamentation occurring both on the arm and theca in several cornutes and mitrates strongly supports the view that the life orientation was similar in all stylophorans and was ‘flat‐surface down’. The presence of an asymmetrical ornamentation adapted to hinder, or minimize, back slippage of the organism in all stylophorans gives strong support to their interpretation as mostly sessile organisms, feeding with the arm facing the current and the theca downstream. The examination of a wide array of thecal morphologies and sculpture patterns displayed by the various groups of cornutes and mitrates allows the identification of three main modes of life in stylophorans: (1) an epibenthic mode of life, with the theca as main anchor to the substrate (e.g. asymmetrical cornutes, Diamphidiocystis); (2) an epibenthic mode of life, with the arm as main anchor to the sediment (e.g. symmetrical cornutes, Peltocystis, primitive Mitrocystitida, some Kirkocystidae); (3) an infaunal mode of life, with the theca buried in a slightly inclined attitude (e.g. some Kirkocystidae, Mitrocystitida with cuesta‐shaped ribs). The partially buried mode of life of Lagynocystis is intermediate between 2 and 3.     

Functional Morphology of the Introvert and Digestive System of Myzostoma cirriferum (Myzostomida)

Myzostoma cirriferum feeds by diverting food particles carried by the ambulacral grooves of its comatulid host Antedon bifida. When searching for food, the myzostome uses its protrusible introvert to fulfil two major functions: sensory perception and the capture of food particles. The digestive system is composed of four parts, viz. a pharynx, that is contained within the introvert, a stomach, a series of paired caeca and an intestine that lie in the myzostome's trunk. The pharynx is supplied with a thick muscle which, thanks to peristaltic movements, carries food particles from the mouth to the stomach. Both stomach and caecal cells are able to absorb dissolved nutriments and to store lipids, whereas intestinal cells are only capable of absorption. Due to the beating of their cilia, stomach cells also carry food particles into the caecal lumen, where they are subjected to endocytosis and intracellular digestion by caecal cells. Undigested food fragments eventually gather in a very large, apical vacuole, and the cell apices containing vacuoles are eliminated into the caecal lumen by an apocrinal process. Detached cell apices reach the stomach, where they are embedded in a matrix, together forming a spindle-shaped faecal mass that is expelled through the postero-ventral anus. The observed digestive process—entailing the regular elimination of the apical part of the caecal digestive cells—appears to be unique among the Spiralia.     

秦岭滑蜥排泄系统组织形态学观察

运用大体解剖和组织切片技术对秦岭滑蜥Scincella tsinlingensis排泄系统进行了组织形态学观察。结果显示:秦岭滑蜥的排泄系统包括肾脏、输尿管、膀胱和泄殖腔。肾脏由被膜与实质构成,实质包括许多泌尿小管与少量结缔组织。泌尿小管包括肾单位与集合管,肾单位的数量较两栖类有了明显增加。结缔组织中分布有少量弹性纤维、网状纤维和大量胶原纤维。输尿管由许多分支的集尿管汇聚形成,包括黏膜与外膜,黏膜由单层柱状上皮过渡为多层鳞状细胞,固有层零散分布有浆细胞,结缔组织中分布有胶原纤维与少量弹性纤维。膀胱由黏膜层、肌层与外膜构成,黏膜上皮为变移上皮,固有层分布有少量的浆细胞。消化道、生殖道和输尿管末端汇聚于泄殖腔,泄殖腔壁由黏膜、肌层和外膜构成,黏膜上皮分布有黏液性细胞和少量浆细胞。秦岭滑蜥的排泄系统与其他卵胎生蜥蜴无明显差别。     

Structure of the Excretory System of Hawaiian Nerites (Gastropoda: Neritoidea)

Neritoidean gastropods are present in freshwater, brackish andmarine environments, which vary in salinity and exposure todehydration. In this study we examine the structure of the excretory systemof Hawaiian nerites, which indicates possible processes thatenable these gastropods to survive in a wide range of environmentsin the Hawaiian Islands. As is true of other nerites studied to date, the main excretorymechanism of Hawaiian nerites is through filtration of the bloodbetween podocytes in the auricle epicardium, resulting in productionof an ultra-filtrate, which collects in the pericardial cavity.No podocytes are present on the surface of the ventricle ofHawaiian nerites. The reno-pericardial canal conveys the urine tothe kidney, the epithelium of which is composed mainly of acidophiliccells in marine nerites. In brackish and fresh water species,baso-philic cells are present in addition to the acidophiliccells present in marine nerites. It is proposed that the basophilickidney cells allows non-marine nerites to osmoregulate and producea hyperosomotic urine at low salinities. A bladder is present,and empties into the mantle cavity near the gill by way of a ureter. (Received 26 November 1997; accepted 15 May 1998)     

A New System for Comparative Functional Genomics of Saccharomyces Yeasts

Whole-genome sequencing, particularly in fungi, has progressed at a tremendous rate. More difficult, however, is experimental testing of the inferences about gene function that can be drawn from comparative sequence analysis alone. We present a genome-wide functional characterization of a sequenced but experimentally understudied budding yeast, Saccharomyces bayanus var. uvarum (henceforth referred to as S. bayanus), allowing us to map changes over the 20 million years that separate this organism from S. cerevisiae. We first created a suite of genetic tools to facilitate work in S. bayanus. Next, we measured the gene-expression response of S. bayanus to a diverse set of perturbations optimized using a computational approach to cover a diverse array of functionally relevant biological responses. The resulting data set reveals that gene-expression patterns are largely conserved, but significant changes may exist in regulatory networks such as carbohydrate utilization and meiosis. In addition to regulatory changes, our approach identified gene functions that have diverged. The functions of genes in core pathways are highly conserved, but we observed many changes in which genes are involved in osmotic stress, peroxisome biogenesis, and autophagy. A surprising number of genes specific to S. bayanus respond to oxidative stress, suggesting the organism may have evolved under different selection pressures than S. cerevisiae. This work expands the scope of genome-scale evolutionary studies from sequence-based analysis to rapid experimental characterization and could be adopted for functional mapping in any lineage of interest. Furthermore, our detailed characterization of S. bayanus provides a valuable resource for comparative functional genomics studies in yeast.     

Protonephridial Excretory System in Vestimentifera (Siboglinidae,Annelida)

Ultrastructural study of the excretory tree of vestimentifera Ridgeia piscesae has shown that it consists of tubules that are blind at their distal ends. The tubules are lined with ciliated cells and have one or two multiciliated terminal cell(s) at the distal ends. In the tubule walls, there are putative ultrafiltration sites. The excretory tree tubules are interpreted as the secondary protonephridia.     

The Functional Morphology of the Recent Brachiopod Bouchardia rosea

Abstract The living terebratellid brachiopod Bouchardia rosea (Mawe), from the southeast Atlantic Ocean, has an unusual internal morphology; both valves are so heavily thickened posteriorly as almost to fill the space, leaving room only for the pedicle, its posterior adjuster muscles and the diductor muscles. These structures are here described in functional terms for the first time and, with the help of partial dissection of the soft tissues, the true nature of the musculature is revealed. Despite its unusual aspects, cardinalial structures of the dorsal valve can be interpreted in terms of those more commonly found in terebratellids. Copyright © 1996 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd.     

Ultrastructural Characteristics of Interneuronal Connections of the Central Nervous System of Bivalve Molluscs

Ultrastructure and peculiarities of interneuronal contacts are studied in visceral ganglia of two species of bivalve molluscs, Anadara broughtoni and Mactra sulcatoria. Gap, desmosome-like, symmetrical, and classic synaptic junctions between neuronal bodies and their main processes are described. The major part of interneuronal junctions in the ganglia of the molluscs studied are symmetrical. Complex synaptic complexes formed by specialized and non-specialized junctions are observed.