摘要:

AbstractThe filum terminale and caudal ampulla of amphioxus were studied by electron microscopy. The filum terminale consists of ependymal cells whose cilia are directed caudally. Remarkably, nerve fibres course through the filum terminale and caudal ampulla and end on the basal lamina forming neuro‐connective structures. Moreover, these nerve boutons are divisible into several classes according to their vesicle content. Boutons containing large dense‐cored vesicles are very similar in appearance to the neurosecretory terminals found in the caudal spinal cord of some vertebrates. These observations on nerve fibres suggest that a primitive neurosecretory system similar to the fish urophysis is present in the amphio

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00318.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe changes that take place in the saccus vasculosus epithelium during smoltification of Atlantic salmon (Salmo salar) are described. The major cell type of the epithelium, the coronet cells, have a number (mean = 32) of spherical protrusions connected with a non‐motile cilium to the apical part of the cell. The protrusions extend into the saccus lumen. In parr the protrusions become more spherical during the spring season, while in smolt the opposite process takes place. Parr coronet cells have most of the mitochondria in the apical part of the cell, while in smolt they are concentrated basally. The relative areal fraction of heterochromatin in the nuclei increase from 23 to 29 during the smoltification process. The results are consistent with the view that the coronet cells take an active part in the smoltification proces

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00319.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe epidermis of the tentacles ofPhoronis australisconsists of six cell types: supporting cells, choanocyte‐like sensory cells, both types monociliated, secretory A‐cells with a mucous secretion, and three kinds of B‐cells with mucoprotein secretions. On cross‐sections of the tentacle, one can distinguish four faces: the frontal one, heavily ciliated and located between the two frontolateral rows of sensory cells, the lateral and the abfrontal ones. The orientation of the basal structures of the cilia is related to the direction of their beat. The basiepidermal nervous system is grouped mainly at the frontal and abfrontal faces. The basement membrane is thickest on the frontal face and consists of circular collagen fibrils near the epidermis and longitudinal ones near the peritoneum. All peritoneal cells surrounding the mesocoel are provided with smooth longitudinal myofibrils, and isolated axons are situated between these cells and the basement membrane. The wall of the single blood capillary in each tentacle consists of epitheliomuscular cells with circular myofilaments, lying on a thin internal basal lamina; there is no endo

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00320.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractBurrowing, iocomotory and other movements of the echiuranOchetostoma caudexhave been examined and discussed. A continuous body cavity enables the worm to undergo peristaltic waves to pump water through the burrow without causing locomotion. The animal is capable of both forward and backward locomotion in its burrow. During forward locomotion, retrograde peristaltic waves are utilized which advance the animal in a step‐wise fashion. Pressure changes within the coelom during burrowing, locomotion and during irrigation movements have been measured with the use of electronic recording techniques and the results interpreted in relation to direct visual observation. The structural and functional specializations for burrowing are discussed and compared with the activities ofPriapulus caudatus, Sipunculus nudusandBonellia viridi

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00321.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe fine structure of the nerve cells and the neuropile in the brain of acoels and the peripheral nervous system and the synapses have been studied. On the basis of the vesicle content, four nerve cell types are distinguished. The presumptive glial cell is also visualized. The synapses appear to be of the following four types: asymmetrical, ribbon, symmetrical and electrical. The peripheral nervous system consists of a subepithelial and a submuscular plexus; they present asymmetrical and symmetrical synapses. In the light of these results, the nervous system of acoels should no longer be considered as primitive.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00322.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractScanning electron microscopy reveals the presence of ciliated epidermal cells that form halos around canal pores and pit lines of the mechanoreceptive lateral line system in two actinopterygian fish,PolypterusandAcipenser.Transmission electron microscopy shows that the cilia exhibit a typical 9 + 2 microtubule configuration and are not directionally polarized. The function, developmental origin and systematic significance of ciliated epidermal cells in actinopterygian fish are considered.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00323.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractSpermatogenesis during post‐metamorphic life in the anadromous parasitic lampreyGeotria australiswas examined in histological sections of testes of animals collected in the field or maintained in the laboratory. The fully metamorphosed downstream migrants ofG. australispossessed a very small testis in which the germ cells consisted of irregularly arranged prospermatogonia. By the end of the subsequent protracted marine trophic phase, the testis had increased in cross‐sectional area by about 20 times and become organised into well‐defined cysts. Since approximately 40% of these cysts possessed spermatocytes and 12% contained spermatids or early sperm, meiosis is initiated prior to the non‐feeding upstream migration, which inG. australislasts for the unusually long period of 15–16 months. The incidence of cysts with meiotic and post‐meiotic stages decreased during the first 3 months of the spawning run before starting to rise during subsequent months. Spermiogenesis was never completed in any animals caught in the field during the first 9 months of the upstream migration or in those subsequently held in the laboratory up to and beyond November, the month when spawning naturally takes place. The phasing and asynchrony of spermatogenesis during post‐metamorphic life inG. australisdiffers markedly from the situation in Northern Hemisp

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00324.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe rostral organ of the coelacanthLatimeria chalumnaecontains a sensory epithelium with luminated ciliated sensory cells, which very much resemble electroreceptors from other non‐teleost fish. This, as well as the innervation and a dorsal nucleus, indicate that this interesting species is electroreceptiv

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00325.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY