摘要:

AbstractAlligator eggs are not turned during incubation, instead the embryo adheres to the top inside of the shell. Turning is alleged to shear off the embryo and kill it. Avian egg turning allegedly facilitates embryonic development by stimulating growth of the area vasculosa and minimizing the effects of unstirred yolk and albumen layers.From day 10 to day 45 of incubation, alligator eggs were experimentally turned, gently, through ± 60° in an hourly cycle. This turning regime killed only 6 out of 25 embryos. Compared with unturned controls, no significant effects were observed on the growth, production of extraembryonic fluids or utilization of albumen and yolk for those embryos that survived turning. The protein concentration of amniotic fluid at various stages of alligator development was examined in eggs incubated at 30 and 33°C. The fluid contained very little protein (max<8 mg) at any time: the protein concentration did not change consistently as development progressed. Differences in response to egg turning in birds and reptiles may be associated with the length of the incubation period, the protein content of the albumen and the mechanism of albumen utilizati

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00938.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIn this paper we describe the larval morphology of two species from the ascidian family Pyuridae,Microcosmus exasperatusandHerdmania momus, with special emphasis on components of the cerebral vesicle. Larvae have not previously been described for any species in the large genusMicrocosmus.Besides a difference in size (larvae ofH. momusare about 40% larger than those ofM. exasperatus), larvae of the two species differ primarily in the number and arrangement of sensory structures. Both species possess a well‐developed statocyte but onlyH. momushas an ocellus. The absence of an ocellus inM. exasperatusis unique among pyurid ascidians. An auxiliary vesicle was found situated on the left side of the cerebral vesicle in both species. However, unlike the larvae ofH. momusand other pyurid species, there is no apparent communication between the auxiliary and cerebral vesicles ofM. exasperatus.Epithelial cells in the auxiliary vesicles of both species carry modified cilia about 2 μm in diameter; auxiliary vesicles ofH. momusalso have simple cilia with axonemes in a 9 + 0 microtubule configuration. InH. momusthe membranes of the epithelial cells are highly convoluted and extend into the lumen of the auxiliary vesicle. Morphological arrangements of auxiliary vesicles and globular cilia reported so far in ascidian tadpoles are contrasted and discuss

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00939.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe terminal part of the protonephridia ofMicrostomumis formed by a branching proximal canal cell and (at least?) two terminal cells. Each weir consists of longitudinal (sometimes convoluted) ribs continuous with the cytoplasm of the terminal cell. Internal leptotriches arise from the terminal and proximal canal cells. Near the tip of the flame, the proximal canal cell tube is surrounded by the more external terminal cell and connected to it by a septate junction. Large cristate mitochondria are densely packed in the terminal and canal cells. The flame bulb ofMicrostomumdiffers markedly from that of other macrostomids (Macrostomum, Paramalostomum) examined. Phylogenetic implications are discussed.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00940.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe Sacoglossa (= Ascoglossa) comprise a ‘complete’ evolutionary series from species with a large shell into which the animal can withdraw completely, through species with a reduced shell covering only the visceral mass, to shell‐less (‘nudibranchiate’) forms some of which have lateral wing‐like extensions, parapodia, others bearing leaf‐like or cylindrical dorsal appendages, cerata. The Sacoglossa are all specialized suctorial feeders, and almost all are stenophagous herbivores. Hence many anatomical adaptations to a particular food occur in the alimentary system. However, a number of characters seem to reflect phylogenetic relationships as well. Among these are presence/absence, shape, and position of pharyngeal pouches, basic shape of radular teeth, branching pattern of digestive gland, and position of anus. The classificatory significance of these characters

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00941.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe spatangoid echinoidEchinocardium cordatumpossesses specialized penicillate podia that handle sediment particles during burrowing and feeding. Epidermal complexes, which occur on podial surfaces directly contacting the sediment, each comprise four cells: a non‐ciliated secretory cell containing granules rich in mucopolysaccharides (NCS cell), a ciliated secretory cell containing granules of unknown composition (CS cell), and two ciliated non‐secretory cells (CNS cells). The cilium of the CS cell is subcuticular whereas that of each CNS cell traverses the cuticle. We propose that these four cells constitute a sensory‐secretory complex wherein the ciliated cells are sensory cells and the secretory cells function for adhesion and de‐adhesion. More exactly, an NCS cell adhesive and a CS cell de‐adhesive would be sequential and would be initiated by two successive stimulations transduced by cilia when the podium touches the sediment. Cilia that first contact the sediment are those protruding through the cuticle from the CNS cells. Their stimulation would result in the secretion of an adhesive material by the NCS cells. Subsequently, the subcuticular cilia of CS cells would be stimulated when the podial digitations closely squeeze the substrate, and this would induce the secretion of a de‐adhesive. These two antagonistic secretions would allow the podium to pick up and discharge sediment repetitively during burrowing

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00942.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe otolith (sagitta) of the chinook salmon (Oncorhynchus tshawytscha) has a variable external crystalline morphology which is related to differences in the growth rate of crystals in different parts of the otolith. The internal crystal structure of the otolith is complex with different mineral phases in different growth fields of the otolith and a well‐defined series of microscopic growth increments in both the dorsal and the ventral parts (orientationin situ) of the otolith. The period of the microscopic growth increments was shown, by both a rearing experiment and interpolation from fish of known age, to be daily. By rearing sibling chinook salmon at different temperatures (while still maintaining them on the same diet) it was shown that the width of the daily growth increment varies with temperature, but neither multi‐ nor sub‐daily increments appear in the area of regular, daily growth incrementation. Inclusions of the vaterite morph of calcium carbonate crystallizing in the botryoidal habit occur in the otherwise aragonitic otolith. Regularly spaced check rings in the sulcul part of the otolith are homologous with those occurring in the dorsal and ventral growth axis and are. on average, separated by about 28 microincre

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1991.tb00943.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY