Abstract:
:Serial sections were used to map the ventrally positioned neurons of the anterior nerve cord of a 12.5-day amphioxus larva from the infundibular region to the end of somite 2. Synaptic patterns reveal five categories of descending pathways, four of which are associated with the ventral compartment (VC) motoneurons responsible for escape swimming. 1) Pre-, para-, and postinfundibular (tegmental) neurons with large varicosities and mixed vesicle populations provide both synaptic and paracrine input to various components of the tegmental neuropile and primary motor center. Four categories of these neurons are distinguished on the basis of their vesicles. 2) Multiple anterior sensory pathways converge on the large paired neurons (LPNs) located near the junction of somites 1 and 2. LPN synaptic output is almost exclusively contralateral. This, together with the evidence for cross-innervation between the third pair of LPNs, is consistent with the latter acting as locomotory pacemakers. 3) Axons from several classes of tegmental neurons converge in the paraxial region on each side of the cord where they form distinct tracts, the upper paraxial bundles. The right bundle is larger than the left, which suggests a role during early development when myotome contractions are biased to one side. 4) Fibers in the ventral tracts from ipsilateral projection neurons, sensory neurons, and additional ascending fibers synapse repeatedly with VC motoneurons. This may be how the overall level of excitation of the latter is controlled so as to modulate their response to pacemaker input. The fifth pathway consists of fibers involved in controlling the dorsal compartment (DC) motoneurons responsible for slow swimming, which are largely isolated from inputs to the VC locomotory system. The ventral neurons of the primary motor center form a more or less continuous file on either side of the floor plate, with certain cell types showing a tendency to cluster. There are, however, few obvious patterns of the kind expected if development were controlled by a rigid, lineage-based mechanism. The evolutionary implications of the involvement of a midbrain-level pacemaker in controlling larval swimming in amphioxus is discussed.
journal_name
J Morpholjournal_title
Journal of morphologyauthors
Lacalli TC,Kelly SJdoi
10.1002/jmor.10114keywords:
subject
Has Abstractpub_date
2003-08-01 00:00:00pages
190-211issue
2eissn
0362-2525issn
1097-4687journal_volume
257pub_type
杂志文章abstract::Septate junctions develop initially just basad from apical junctional complexes at the apical ends of regenerating gastrodermal cells. The first morphological indication of differentiation of the junction is the appearance of gentle undulations of the plasma membranes of apposing cells. Subsequently dense dots develop...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051920303
更新日期:1987-06-01 00:00:00
abstract::Mate, prey, and predator recognition often depend on the integration of information from multiple sensory modalities including visual, auditory, and/or olfactory inputs. In Crotalinae, the eyes sense visible light while the pit organs detect infrared (IR) radiation. Previous studies indicate that there is significant ...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.20483
更新日期:2016-01-01 00:00:00
abstract::External features of the egg, developing embryo, and first instar nymph of Kamimuria tibialis are described. The embryonic development from the germ disc to the full-grown embryo is divided into 12 stages. The saclike embryonic rudiment is formed by the bending and folding of the germ disc. The embryo first elongates ...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051830308
更新日期:1985-03-01 00:00:00
abstract::The morphology of the spermatozoon of representative species of the subfamily Nesomyinae (Muroidea: Nesomyidae), a monophyletic group of rodents endemic to Madagascar, was examined by light and electron microscopy to determine the sperm head shape and tail length across the species. Marked interspecific differences we...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.10889
更新日期:2010-12-01 00:00:00
abstract::The Puerto Rican tree frog, Eleutherodactylus coqui, has internal fertilization and direct development on land. In light of these reproductive adaptations, the events of fertilization and early development were studied. Cytological examination of just-fertilized eggs showed that sperm entry is restricted to about 10% ...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051930208
更新日期:1987-08-01 00:00:00
abstract::Although mating has been described in several hermit crab species, the mechanics of spermatophore transfer have not previously been demonstrated. Evidence from pleopod and gonopore morphology, video observations, and inseminated females indicates that in Clibanarius vittatus the male applies a spermatophoric mass dire...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1118
更新日期:2002-08-01 00:00:00
abstract::The fate and possible roles of the cytoskeleton in the process of conjugation in the hyptrich ciliate Euplotes aediculatus were investigated. Following the coalescence of the plasma membranes of the conjugant cells, a fusion zone or bridge of cytoplasm contributed by both partners is constructed. The sub-alveolar micr...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051920104
更新日期:1987-04-01 00:00:00
abstract::The architectural ground plan of beetle and other insect midguts is represented by a monolayer of epithelial cells arranged in a cylindrical configuration. Proliferation and differentiation of regenerative cells maintain the integrity of this monolayer in the face of continual losses of individual cells through cytopl...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.20038
更新日期:2012-09-01 00:00:00
abstract::Over the past few decades, geometric morphometric methods have become increasingly popular and powerful tools to describe morphological data while over the same period artificial neural networks have had a similar rise in the classification of specimens to preconceived groups. However, there has been little research i...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.20626
更新日期:2017-01-01 00:00:00
abstract::Larval salivary gland cells of seven Drosophila species from the melanogaster group were studied during the early third-instar period. Similar cytoplasmic organization was seen in both the distal and proximal parts of the gland. The cytoplasm contained a large number of free ribosomes, but only a few rough endoplasmic...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051980109
更新日期:1988-10-01 00:00:00
abstract::The orientation of the semicircular canals of the inner ear in the skull of vertebrates is one of the determinants of the capacity of this system to detect a given rotational movement of the head. Past functional studies on the spatial orientation of the semicircular canals essentially focused on the lateral semicircu...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.20665
更新日期:2017-05-01 00:00:00
abstract::Scanning electron microscopy reveals that the flat tongue of Platemys pallidipectoris has shallow grooves and no lingual papillae. The surface of the tongue is covered with dome-shaped bulges, each corresponding to a single cell. Short microvilli are distributed over the cell surface. Light microscopy shows a stratifi...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1052260303
更新日期:1995-12-01 00:00:00
abstract::The coiled shell of gastropods begins as a cap-shaped lens of organic and calcified material that covers the posterior dorsal side of the larva. During development the cap enlarges to cover the larval visceral mass. Marginal growth then produces the characteristic coiled shell. One model of the initiation of shell coi...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/(SICI)1097-4687(199801)235:1<77::AID-JMOR6
更新日期:1998-01-01 00:00:00
abstract::In this study, we compare and contrast armoring strategies during early ontogeny among three related species of marine turtles: the hawksbill, a species that diverged about 29 mya from the loggerhead and Kemp's ridley, which diverged from one another about 16 mya. Our purpose was to determine whether there was a corre...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.20844
更新日期:2018-09-01 00:00:00
abstract::The sagittal otolith of Hyperoglyphe antarctica (Centrolophidae: Teleostei) has a prismatic structure in which the anti-sulcal growth axes of each prism consist of a series of nested cones each composed of a mineral layer followed by an organic matrix layer. Broken sections show the mineral layers to be composed of st...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1052230208
更新日期:1995-02-01 00:00:00
abstract::This descriptive electron microscopic study of the blastogenetic medusa development of Podocoryne carnea focuses on the earliest stages of primordium formation, myogenesis, oogenesis and cnidogenesis. The events which take place at the cellular level prior to the formation of stage 1 (Frey, '68), which are characteriz...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051540206
更新日期:1977-11-01 00:00:00
abstract::The usual pigmentation pattern in mammalian skin consists of fixed melanocytes in the basal layer of the epidermis, supplying keratinocytes with melanosomes. We observed that the glabrous skin (rhinaria and footpads) of dogs deviates from this pattern. In dogs, melanocytes are found in both the dermis and epidermis. T...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.20842
更新日期:2018-08-01 00:00:00
abstract::Topological and histological analyses of Mabuya mabouya embryos at different developmental stages showed an extraembryonic membrane sequence as follows: a bilaminar omphalopleure and progressive mesodermal expansion around the whole yolk sac at gastrula stages; mesodermal split and formation of an exocoelom in the ent...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.10138
更新日期:2003-11-01 00:00:00
abstract::Motor units of the medial gastrocnemius (MG) and the single lateral gastrocnemius/soleus (LG/S) muscles of the opossum (Didelphis virginiana) were found to have uniformly slow contraction times relative to homologous muscles of the cat. Though a broad range of peak tetanic tensions was found among motor units from bot...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051810305
更新日期:1984-09-01 00:00:00
abstract::Interspecific variations in rhabdom structure between various oplophorid shrimps are described and the differences are related to the light environment at different depths within the mesopelagic zone. The ultrastructure of the distal rhabdom in these species is described for the first time. Quantitative measurements s...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.10103
更新日期:2003-07-01 00:00:00
abstract::All developmental stages of Tanystylum bealensis are described. This is the first complete developmental series of a pycnogonid species collected from a natural, rather than a laboratory-reared population. Development proceeds through a series of nine instars from egg to adult, with major defining characteristics of t...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.10402
更新日期:2006-03-01 00:00:00
abstract::The light microscopic analysis of serial sections of the subcommissural organ (SCO) of the rainbow trout (Salmo gairdneri) shows that the form of the groove-like (in cross section) organ varies over its total length. Its rostral origin is a tunnel-like structure anterior to the orifice of the hollow pineal stalk. The ...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051960307
更新日期:1988-06-01 00:00:00
abstract::Tooth development and replacement in fetal and adult viviparous caecilians (Amphibia: Gymnophiona) are described and analyzed according to current theories of tooth succession. The fetal dentition differs from that of the adult in morphology, position, and function. Teeth are used by fetuses to scrape the oviducal epi...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051480104
更新日期:1976-01-01 00:00:00
abstract::Intraspecific trends in freshwater mussel (unionoid) shells that are consistently associated with differences in the mussels' sex and/or parasitic infestation can potentially be used to reconstruct sex ratios or parasitic levels of modern and ancient unionoid populations. In contrast to morphological patterns within m...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.10990
更新日期:2011-11-01 00:00:00
abstract::Ventral bars, cartilaginous projections from the ventral aspect of the synsacrum that contact and form a joint with the ilium, were found in all normal chick embryos of age E9 and older. Bars were absent in a number of embryos which had been paralyzed from age E4 by the use of the acetylcholine receptor blocker alpha-...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051730205
更新日期:1982-08-01 00:00:00
abstract::The overall anatomy of Neodasys as well as data for hemoglobin-containing cells are described. Hemoglobin-containing cells are shown to be mesodermal specializations constituting approximately 14% of the animal's total body volume (4.87 ± 104 μl). These globular cells (10-14 μm) are situated in two longitudinal rows, ...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051750106
更新日期:1983-01-01 00:00:00
abstract::The ultrastructure of the coxal glands and associated tissues in the centipedes Lithobius forficatus and Lithobius crassipes has been examined in the light of two contrasting functional hypotheses postulated by different authors. Lithobiomorph chilopods possess eight sets of pores on the posterioventral border of the ...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051770204
更新日期:1983-08-01 00:00:00
abstract::Swimming crabs of the taxon Portunoidea show specialized, paddle-shaped fifth pereiopods (P5), which play a role in these crabs' ability to swim. In this study, the morphology of the fifth pereiopod in swimming and non-swimming crabs was studied in detail and the mobility in the articulations between podomeres was cal...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.21268
更新日期:2020-12-01 00:00:00
abstract::Neurosecretory (Nsy) cells within the cerebral ganglion of Lumbricus terrestris were classified ultrastructurally. The Nsy cells within the subesophageal ganglion, nerve cord ganglion, and the peripheral nervous system were also examined. A comparative survey of Nsy cells of four other species of oligochaetes, Eisenia...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051970102
更新日期:1988-07-01 00:00:00
abstract::The functional anatomy of the hindlimb of 12 species of viverrids was studied with relation to locomotion. The animals were allocated to primary locomotor categories on the basis of their anatomy and locomotion. The climbing, arboreal walking category (Nandinia binotata) is characterized by a small sacroiliac articula...
journal_title:Journal of morphology
pub_type: 杂志文章
doi:10.1002/jmor.1051480208
更新日期:1976-02-01 00:00:00