摘要:

AbstractFMRFamide‐like immunoreactivity has been demonstrated in the digenean trematodeEchinostoma liei.The functions of FMRFamide‐like substances appear to be many and varied within the invertebrates, where they are involved in neurotransmission, cardiovascular regulation, muscular contraction and/or relaxation, and in co‐ordination of growth and maturation. It is clearly indicated that FMRFamide‐like substances function as neurotransmitter/neuromodulator inE. lieiby the abundance of positively stained nerve fibres and perikarya seen throughout the CNS and PNS. A single endocrine‐like cell also showing FMRFamide‐like immunoreactivity is situated within the muscular c

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00311.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe freely spawned eggs ofCraniago through radial cleavage, embolic gastrulation, and the posteroventral part of the archenteron forms mesoderm through modified enterocoely. The blastopore closes in the posterior end of the larva. The ciliated, lecithotrophic larva has four pairs of coelomic pouches and three pairs of dorsal setal bundles. At metamorphosis, the larva curls ventrally by contraction of a pair of midventral muscles, which are extensions of the first pair of coelomic sacs; the larva attaches by the epithelium just behind the closed blastopore. The brachial valve is secreted by the middle part of the dorsal epithelium and the pedicle valve is secreted by the attachment epithelium. The second pair of coelomic sacs develop small attachment areas at the edge of the dorsal valve and become the lophophore coelom (mesocoel); the third pair of coelomic sacs become the body coelom (metacoel) with the adductor muscles. The posterior position of the closing blastopore is characteristic of deuterostomes. The ventral curving of the settling larva and the formation of both valves from dorsal epithelial areas indicate that the brachiopods have a very short ventral side as opposed to the phoronids. It is concluded that both groups have originated from a creeping ancestor with a straight gut.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00312.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractHolthuisana transversareabsorbs much of its exoskeletal calcium in the last 3 days before ecdysis and stores it in circulating granules in the haemocoel and in non‐circulating granules in the subepidermal connective tissue. Calcium enters the epidermal cells from the moulting fluid, probably through their apical microvilli and is either incorporated into intracellular calcium granules or exits the cell via the basolateral membranes to be used in formation of two other granule types. Intracellular granules (0.4–2 μm long) form in large masses in the apical cytoplasm of the epidermal cells. They are formed as membrane‐bound vesicles by the Golgi, and calcium and organic matrix material are added from the surrounding cytoplasm. As development proceeds, lamellae appear and calcium carbonate is deposited in the matrix. Granule masses move basally and are stored in the connective tissue. Calcium is also incorporated into extracellular large granules (0.8–3.8 μm long) which are formed in narrow intercellular channels between epidermal cells. A third granule type (small granules, 0.26 μm diameter) is formed in subepidermal connective tissue cells and released into the haemolymph in very large numbers. Calcium was identified in the two larger granule types using X‐ray microanalysis and significant amounts of phosphorus and potassium were also present in the large granules. A model for ion cycling between the exoskeleton and granules

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00313.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractTwo hitherto unknown ligaments that assist in holding the brain in position occur in the brachiopterygian fishPolypterus senegalus.These rounded fibrous cords, placed one behind the other, are called ligamentum intracraniale transversum and ligamentum intracraniale obliquum. The former spans the orbitotemporal division of the cranial cavity and passes through the velum transversum. The latter, which is paired, extends from the roof to the sidewall of the endocranium and runs in the rhombomesencephalic sulcus in company with the trochlear nerve. It is argued that these intracranial ligments, like the spinal denticulate ligaments, are derivatives of a pair of fibrous bands which in early craniate phylogeny extended throughout the length of the neuraxial meninx and enhanced its tensile strength. It is also argued that at least the transverse intracranial ligament was already in existence some 350 million years ago.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00314.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractStructural alterations accompanying the development of germ cells in representatives of two families of gamasid mites: Pergamasidae (Pergumasus barbarus. P. truatellus) and Parasitidae (Porrhostaspis lunulata) were examined by scanning electron microscopy. Spermatogenesis occurs in cysts containing two (P. lunuluta) or four spermatogonia (P. barbarusandP. truatellus) prior to meiosis. later arranged in a tetrahedral pattern. Meiosis produces 8 and 16 spermatids per cyst, respectively. Spermatids are located radially and elongate synchronously. Dimples appear at their acrosomal ends, soon replaced by peg‐like structures surrounded by superficial ridges. The number of ridges which correspond to longitudinal ribbons can vary between and within species as well as between spermatids occupying one cyst. Our observations suggest some unknown mechanism which allows the spermatozoa to enter vasa deferentia in a unidirectional orientatio

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00315.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractInPegea, scanning electron microscopy of what appear to be the least damaged portions of the filter shows that it has a regular rectangular mesh consisting of thick (100 nm) fibres at right angles to thinner (50 nm) fibres. The rectangular pores of the filter are around 3.3 × 0.57 μm. These measured values from filters that have suffered shrinkage (to an uncertain degree) during preparation are considered to indicate that the actual pore size in life is some 4.0 × 0.7 μm. The mucous‐net feeding filter of salps differs from that of other tunicates since flow through it results from muscular activity. Calculations based on the estimated pore size and filtering rate suggest that during part of the filtering cycle, the pressure drop across the filter is considerably greater than that across other tunicate mucous‐net

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00316.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Book reviewed in this article:Nikam, J. B.&Khole, V. V. 1989.Insect spiracular systems.K. G. Adiyodi&R. G. Adiyodi (eds). 1989.Reproductive biology of invertebrates, Vol. IV. Fertilization, development and parental care, Part A.Ax, P. 1987.The phylogenetic system.—The systematization of organisms on the basis of their phylogenesis.Translated by R. P. S. Jefferie

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00317.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY