The early life of Octopus vulgaris (Cephalopoda: Octopodidae) in the plankton and at settlement: a change in lifestyle

Newly hatched young of the benthic, coastal-living octopod, Octopus vulgaris , enter the plankton and remain there for perhaps eight weeks. At hatching the arms are short and bear a few, large, primary suckers. The buccal mass is relatively large in proportion to the size of the animal. The eyes are large. The central nervous system has fairly well-defined lobes, some of which develop earlier than others. We shall follow the development of several features of O. vulgaris from hatching, through its life in the plankton until settlement and correlate them with changes in the brain and behaviour.     

Development of the eye and optic lobe of Octopus

The development of the lens, retina and optic lobes was followed in Octopus australis and O. pallidus , two species that produce benthic larvae and can readily be reared in the laboratory from egg to adult.
The inner part of the lens starts to form at Naef's stage IX, and consists of a central core with overlying layers formed from processes of the lentigenic cells. Microvilli occur on the surface of the lens, and cilia and microvilli are visible in the retina, which at this point, however, is undifferentiated. The optic lobes have not started to form. The outer part of the lens starts to develop from stage XVI.
Cellular differentiation of the retina, through cell nuclei crossing the basement membrane, starts at stage XV, with rhabdome development occurring from stage XVI onwards. The optic lobes are clearly formed at stage XII, but only start to differentiate and show layering from stage XVI.
At hatching all adult structures are clearly visible, although considerable quantitative changes still occur before the final adult form is reached.
The development of the visual system of Octopus is similar to that of several species of decapod previously reported.     

The VD1/RPD2 α1-neuropeptide is highly expressed in the brain of cephalopod mollusks

In certain gastropod mollusks, the central neurons VD(1) and RPD(2) express a distinct peptide, the so-called VD(1)/RPD(2) α1-neuropeptide. In order to test whether this peptide is also present in the complex cephalopod central nervous system (CNS), we investigated several octopod and squid species. In the adult decapod squid Idiosepius notoides the α1-neuropeptide is expressed throughout the CNS, with the exception of the vertical lobe and the superior and inferior frontal lobes, by very few immunoreactive elements. Immunoreactive cell somata are particularly abundant in brain lobes and associated organs unique to cephalopods such as the subvertical, optic, peduncle, and olfactory lobes. The posterior basal lobes house another large group of immunoreactive cell somata. In the decapod Idiosepius notoides, the α1-neuropeptide is first expressed in the olfactory organ, while in the octopod Octopus vulgaris it is first detected in the olfactory lobe. In prehatchlings of the sepiolid Euprymna scolopes as well as the squids Sepioteuthis australis and Loligo vulgaris, the α1-neuropeptide is expressed in the periesophageal and posterior subesophageal mass. Prehatchlings of L. vulgaris express the α1-neuropeptide in wide parts of the CNS, including the vertical lobe. α1-neuropeptide expression in the developing CNS does not appear to be evolutionarily conserved across various cephalopod taxa investigated. Strong expression in different brain lobes of the adult squid I. notoides and prehatching L. vulgaris suggests a putative role as a neurotransmitter or neuromodulator in these species; however, electrophysiological evidence is still missing.     

Structure of the extraembryonic matrices around the benthic embryos of Patiriella exigua (Asteroidea) and their roles in benthic development: Comparison with the planktonic embryos of Patiriella regularis

The extracellular matrices (ECMs) surrounding the benthic embryos and larvae of the seastar Patiriella exigua and the planktonic embryos of Patiriella regularis were examined by transmission and scanning electron microscopy. Three ECMs surround unhatched embryos: An outer jelly coat, a fertilization envelope, and an inner hyaline layer. The ECMs of P. exigua are modified for supporting benthic development. The dense jelly coat attaches the embryo to the substratum, and the fertilization envelope forms a though protective case. In comparison, P. regularis has a less dense jelly coat and a thinner fertilization envelope. The hyaline layer of both species is comprised of three main regions: An intervillous layer overlying the epithelium, a supporting layer, and a coarse meshwork layer. Unhatched P. exigua have an additional outer amorphous layer that adheres to the fertilization envelope. As a result, the hyaline layer forms a continuous ECM that unites the embryonic surface with the fertilization envelope. Embryos of P. exigua removed from their fertilization envelopes lack the outer amorphous region, have a poorly developed hyaline layer, and do not develop beyond gastrulation. It appears that the substantial hyaline layer of P. exigua and its attachment to the fertilization envelope are essential for early development and that this ECM may function as a gelatinous cushioning layer around the benthic embryos. At hatching, the amorphous layer is discarded with the envelope. In contrast, an amorphous layer is absent from the hyaline layer of P. regularis. The demembranated embryos of this species have an ECM similar to that of controls and develop normally to the larval stage. © 1995 Wiley-Liss, Inc.     

NS-4 (nervous system antigen-4), a cell surface antigen of developing and adult mouse brain and sperm.

Morphological changes in the chorion of the Medaka, Oryzias latipes, brought about by the hatching enzyme were examined by transmission as well as scanning electron microscopy. The structure of the intact chorion, especially its thick multilamellar inner layer, does not change during development until about 1 hr before the onset of hatching. As choriolysis proceeds, the inner layer of the chorion is digested to yield soluble proteins of relatively high molecular weight. During this process it appears that each lamella is successively solubilized from the inner surface of the chorion. Finally, a thin outer layer with accompanying villi and attaching filaments remains.Under the experimental conditions used, the enzyme was in direct contact with both the inner and outer layers of the chorion. Because of this, the enzyme could penetrate the outer layer and act on some peripheral parts of the underlying inner layer. Based on these morphological changes, a mechanism is proposed to account for the solubilization of the chorion by the hatching enzyme.     

Ontogenetic Shape Change in the Chicken Brain: Implications for Paleontology

Paleontologists have investigated brain morphology of extinct birds with little information on post-hatching changes in avian brain morphology. Without the knowledge of ontogenesis, assessing brain morphology in fossil taxa could lead to misinterpretation of the phylogeny or neurosensory development of extinct species. Hence, it is imperative to determine how avian brain morphology changes during post-hatching growth. In this study, chicken brain shape was compared at various developmental stages using three-dimensional (3D) geometric morphometric analysis and the growth rate of brain regions was evaluated to explore post-hatching morphological changes. Microscopic MRI (μMRI) was used to acquire in vivo data from living and post-mortem chicken brains. The telencephalon rotates caudoventrally during growth. This change in shape leads to a relative caudodorsal rotation of the cerebellum and myelencephalon. In addition, all brain regions elongate rostrocaudally and this leads to a more slender brain shape. The growth rates of each brain region were constant and the slopes from the growth formula were parallel. The dominant pattern of ontogenetic shape change corresponded with interspecific shape changes due to increasing brain size. That is, the interspecific and ontogenetic changes in brain shape due to increased size have similar patterns. Although the shape of the brain and each brain region changed considerably, the volume ratio of each brain region did not change. This suggests that the brain can change its shape after completing functional differentiation of the brain regions. Moreover, these results show that consideration of ontogenetic changes in brain shape is necessary for an accurate assessment of brain morphology in paleontological studies.     

Neuropeptide Y-immunoreactive neuronal system and colocalization with FMRFamide in the optic lobe and peduncle complex of the octopus (Octopus vulgaris)

The distribution of neuropeptide Y (NPY)-like immunoreactivity and its colocalization with FMRFamide were investigated in the optic lobe and peduncle complex of the octopus ( Octopus vulgaris) by using immunohistochemical techniques. In the optic lobe cortex, NPY-immunoreactive (NPY-IR) fibers were observed in the plexiform layer, although no NPY-IR somata were observed in the outer or inner granular cell layers. In the optic lobe medulla, NPY-IR somata were seen in the cell islands, and abundant NPY-IR varicose fibers were observed in the neuropil. Most of the NPY-IR structures in the medulla showed FMRFamide-like immunoreactivity. In the peduncle lobe, abundant NPY-IR and FMRFamide-IR (NPY/FMRF-IR) varicose fibers were seen in the basal zone neuropil of the peduncle lobe. In the olfactory lobe, NPY/FMRF-IR varicose fibers were also abundant in the neuropil of the three lobules. NPY/FMRF-IR somata, with processes running to various neuropils, were scattered in the median and posterior lobules. In the optic gland, many NPY/FMRF-IR varicose fibers formed a honeycomb pattern. These observations suggest that NPY/FMRF-IR neurons in the optic lobes participate in the modulation of visual information and that those in the optic gland are involved in the regulation of endocrine function.     

Amphiphile induced echinocyte-spheroechinocyte transformation of red blood cell shape

A possible physical explanation of the echinocyte-spheroechinocyte red blood cell (RBC) shape transformation induced by the intercalation of amphiphilic molecules into the outer layer of the RBC plasma membrane bilayer is given. The stable RBC shape is determined by the minimization of the membrane elastic energy, consisting of the bilayer bending energy, the bilayer relative stretching energy and the skeleton shear elastic energy. It is shown that for a given relative cell volume the calculated number of echinocyte spicula increases while their size decreases as the number of the intercalated amphiphilic molecules in the outer layer of the cell membrane bilayer is increased, which is in agreement with experimental observations. Further, it is shown that the equilibrium difference between the outer and the inner membrane leaflet areas of the stable RBC shapes increases if the amount of the intercalated amphiphiles is increased, thereby verifying theoretically the original bilayer couple hypothesis of Sheetz and Singer (1974) and Evans (1974). Received: 22 August 1997 / Revised version: 25 November 1997 / Accepted: 11 February 1998     

The ontogeny of shell secretion in Terebratalia transversa (Brachiopoda, Articulata). I. Development of the mantle

The morphology of the mantle in free-swimming and metamorphosing larvae of the articulate brachiopod Terebratalia transversa has been examined by scanning and transmission electron microscopy. The mantle begins to form approximately 2 days after fertilization and subsequently develops into a skirtlike lobe that encircles the middle region of the larval body. A simple epithelium covers both the outer surface of the mantle lobe and the inner side situated next to the pedicle lobe of the larva. During metamorphosis, the mantle lobe is everted over the anterior end of the larva. Thus, the epithelium covering the outer part of the mantle lobe in the larva subsequently becomes the inner epithelium of the juvenile mantle. Similarly, the inner epithelium of the larval mantle lobe represents the future outer epithelium of the juvenile mantle. In free-swimming larvae, the prospective outer mantle epithelium contains two types of cells, called "lobate" and "vesicular" cells. Lobate cells initially deposit a thin layer of amorphous material, and vesicular cells produce ovoid multigranular bodies. Following settlement at about 5 days postfertilization, the vesicular cells secrete an electron-dense sheet that constitutes the basal layer of the developing periostracum. Within several hours to a day thereafter, reversal of the mantle lobe is rapidly effected, apparently by contractions of the pedicle adjustor muscles.     

Ultrastructure of the embryonic snake skin and putative role of histidine in the differentiation of the shedding complex.

The morphogenesis and ultrastructure of the epidermis of snake embryos were studied at progressive stages of development through hatching to determine the time and modality of differentiation of the shedding complex. Scales form as symmetric epidermal bumps that become slanted and eventually very overlapped. During the asymmetrization of the bumps, the basal cells of the forming outer surface of the scale become columnar, as in an epidermal placode, and accumulate glycogen. Small dermal condensations are sometimes seen and probably represent primordia of the axial dense dermis of the growing tip of scales. Deep, dense, and superficial loose dermal regions are formed when the epidermis is bilayered (periderm and basal epidermis) and undifferentiated. Glycogen and lipids decrease from basal cells to differentiating suprabasal cells. On the outer scale surface, beneath the peridermis, a layer containing dense granules and sparse 25-30-nm thick coarse filaments is formed. The underlying clear layer does not contain keratohyalin-like granules but has a rich cytoskeleton of intermediate filaments. Small denticles are formed and they interdigitate with the oberhautchen spinulae formed underneath. On the inner scale surface the clear layer contains dense granules, coarse filaments, and does not form denticles with the aspinulated oberhautchen. On the inner side surface the oberhautchen only forms occasional spinulae. The sloughing of the periderm and embryonic epidermis takes place in ovo 5-6 days before hatching. There follow beta-, mesos-, and alpha-layers, not yet mature before hatching. No resting period is present but a new generation is immediately produced so that at 6-10 h posthatching an inner generation and a new shedding complex are forming beneath the outer generation. The first shedding complex differentiates 10-11 days before hatching. In hatchlings 6-10 h old, tritiated histidine is taken up in the epidermis 4 h after injection and is found mainly in the shedding complex, especially in the apposed membranes of the clear layer and oberhautchen cells. This indicates that a histidine-rich protein is produced in preparation for shedding, as previously seen in lizard epidermis. The second shedding (first posthatching) takes place at 7-9 days posthatching. It is suggested that the shedding complex in lepidosaurian reptiles has evolved after the production of a histidine-rich protein and of a beta-keratin layer beneath the former alpha-layer.     

Post-hatching development of the thymic epithelial cells in the rainbow trout Salmo gairdneri: an ultrastructural study

This study reports the ultrastructure of subpopulations of epithelial cells of the thymic parenchyma during the post-hatching development of the rainbow trout, Salmo gairdner, kept at 14 degrees C. At hatching, the thymus contained a small number of medium and large thymocytes interspersed among three different types of epithelial cells: (1) epithelial cells adjacent to the connective tissue capsule; (2) ramified dark epithelial cells with electron-dense cytoplasm; and (3) pale electron-lucent epithelial cells displaying secretory-like features. All these cells types were anchored to one another by desmosomes and had apparently differentiated from the pharyngeal epithelium. At 4 days after hatching, the thymus enlarged, and numerous gaps occurred between the cell processes of contiguous epithelial cells adjacent to the capsular connective tissue. In 21-day-old trout, thymic trabeculae developed carrying blood vessels, and a subcapsular zone became evident containing lymphoblasts and large subcapsular epithelial cells. In 30-day-old trout, an outer thymic zone developed consisting of spindle-shaped epithelial cells which formed a dense network. At this stage, scattered cystic cells, which apparently differentiated from the pale epithelial cells, were present.     

Structure and development of the larval visual system in embryos of Lytta viridana leconte (coleoptera,meloidae)

At hatching (252–264 hr. at 25 ± 0.5°C), the visual system in larvae of Lytta viridana consists of paired stemmata, stemmatal nerves, optic neuropiles, and inner and outer imaginal optic lobe anlagen. It originates between 64 and 72 hr. with invagination of an optic lobe primordium in the side of each protocephalic lobe. These primordia later differentiate into protocerebral ganglion cells and the imaginal optic lobe anlagen. Each stemma arises at 72 hr. from epidermis below and behind the optic lobe invagination and subsequently becomes cupshaped, closes over, and differentiates. At hatching, it consists of a planoconvex corneal lens, a corneagenous layer, and an everse retina of numerous, pigmented retinular cells, each with a terminal rhabdomere. Between 96 and 104 hr, proximal ends of the retinular cells grow posteromedially into a transverse, horizontal fold in the posterior wall of each optic lobe invagination and along its length to the protocerebral neuropile, which they contact by 112 hr. As the brain withdraws posteriorly within the head, these axons elongate correspondingly. Sheath cells of stemmata and stemmatal nerves descend either from protocerebral perineurium or the optic lobe primordia. Structure and development of the larval visual system in L. viridana are compared with those of other insects and its various components are shown to be homologous throughout the Insecta. However, the stemmata of this insect more closely resemble the atypical imaginal eyes of male scale insects than the photoreceptors of other holometabolous larvae–a similarity arising through convergence.     

Normal neuroanatomical variation in the human brain: an MRI-volumetric study

Normative data on the in vivo size of the human brain and its major anatomically defined subdivisions are not readily available. In this study, high-resolution magnetic resonance imaging was used to measure regional brain volumes in 46 normal, right-handed adults (23 men, 23 women) between the ages of 22-49 years. Parcellation of the brain was based on neuroanatomical landmarks. The following brain regions were measured: the cerebral hemispheres, frontal lobe, temporal lobe, parietal lobe, occipital lobe, cingulate gyrus, insula, cerebellum, corpus callosum, and lateral ventricles. Males tend to be significantly larger than females, for the whole brain and for nearly all of its major subdivisions, including the corpus callosum. However, the proportional sizes of regions relative to total volume of the hemisphere are remarkably similar in males and females. Variation in size of region is always greater than variation in proportional representation. Asymmetries in brain regions are not profound, with the exception of the cingulate gyrus, which is larger in the left hemisphere. Brain regions are highly correlated in size, with the exception of the lateral ventricles. After controlling for hemisphere size, the volumes of the frontal and parietal lobes are significantly negatively correlated. The occipital lobe tends to be less sexually dimorphic than other major lobes, and less correlated with other brain regions for volume. These results have implications for understanding whether or not certain sectors of the brain have shown relative expansion over the course of hominid and hominoid evolution.     

Ultrastructural aspects of the surface coatings of eggs and larvae of the starfish,Pisaster ochraceus,revealed by alcian blue

Eggs of the asteroid Pisaster ochraceus demonstrate cortical granules, a thick vitelline membrane, and a poorly stained jelly coat similar to that seen on the eggs of other echinoderms. When fixed in the presence of alcian blue the jelly coat is seen to be made up of three regions, an inner layer consisting of a meshwork of fibres, a middle layer of thicker fibres, and a dense outer layer. At fertilization the cortical granules release their contents into the potential space between the vitelline layers and a low fertilization membrane consisting of the vitelline layer and a dense component of the corticle granule is formed. Initially the remaining contents of the corticle granules form an amorphous hyaline layer that fills the space between the plasma membrane and the fertilization membrane. At hatching a distinct hyaline layer is present. It persists at least to the bipinnaria stage and consists of four distinct layers. A similar layer is also located over much of the early embryonic endoderm but is lost from the regions involved in the formation of the mesenchyme cells, coelom, and mouth just before these events take place. Numerous large clear vesicles are located in the apex of all cells associated with a hyaline layer. Where the hyaline layer is lacking, only scattered vesicles are present suggesting that the vesicles may be involved in maintenance of the layer. Attempts to identify elements of the hyaline layer by immunofluorescence demonstrated that it appears to bind both antisera and control sera in a nonspecific manner.     

Hatching of an estuarine crab, Sesarma haematocheir: from disappearance of the inner (E3) layer to rupture of the egg case

Hatching of decapod crustaceans is characterized by the sudden rupture of the egg case. This study focused on the following two issues regarding the hatching mechanism of the estuarine terrestrial crab Sesarma haematocheir: (1) dissolution of the egg case, and (2) the site where the egg case breaks. The egg case comprises three layers: the outer two (E1 and E2) layers and the inner (E3) thin layer (0.2 microm in thickness). The outer layers showed no morphological changes upon hatching, but the inner layer (E3) was markedly digested. The digestion of this layer would enable the embryo to absorb ambient water via reverse peristalsis of the intestine, resulting in an increase of the volume. The egg case always ruptured perpendicular to the longitudinal axis of the embryo. In addition, breakage of the egg case occurred at the dorsal thorax of the embryo. The three major organs positioned at this area were (1) a sharp projection (dorsal spine), (2) an assemblage of muscles, and (3) a pair of secretory glands, each of which was about 30 microm in diameter. The dorsal projection is soft before hatching, and it is clear that the egg case does not break with the posterior expansion of this projection. The rupture instead appears to be caused by the expansion of the muscles arranged perpendicular to the body axis. In addition, some (unknown) factor might weaken the egg case just before hatching. The secretory glands may be a kind of rosette gland, but the role that this gland plays at hatching is not known. As a duct comes out from the center and enters the dorsal projection, some active substance may be released at the tip of this projection. However, immunochemical studies are not consistent with this substance being an ovigerous hair stripping substance (OHSS).     

Ovulation order mediates a trade-off between pre-hatching and post-hatching viability in an altricial bird

Simultaneously dependent siblings often compete for parentally provided resources. This competition may lead to mortality, the probability of which may be a function, in part, of the individual offspring's production order. In birds, serial ovulation followed by hatching asynchrony of simultaneous dependents leads to differences in post-hatching survival that largely depend on ovulation (laying) order. This has led to the widespread assumption that early-laid eggs are of greater value and therefore should possess different maternally manipulated characteristics than later-laid eggs. However, this perspective ignores the potential effect of laying order on pre-hatching viability, an effect which some studies suggest should offset the effect of laying order on post-hatching viability. I examined the relationship between laying order and hatching and fledging probability in wild, free-living Lincoln's sparrows (Melospiza lincolnii). In broods with complete hatching success, first-laid and therefore first-hatched offspring had the highest probability of fledging, and fledging probability declined with increasing laying order. However, first-laid eggs were less likely than later-laid eggs to hatch. This effect of laying order on pre-hatching viability seemed to offset that on post-hatching viability, and, consistently, maternal investment in egg size varied little if at all with respect to laying order. These results suggest that ovulation order mediates a trade-off between pre-hatching and post-hatching viability and should encourage a re-evaluation of the solitary role post-embryonic survival often plays when researchers make assumptions about the value of propagules based on the order in which they are produced.     

Activation of the serotonergic system in chick spinal cord during hatching.

The objectives of the present study were to determine the levels of serotonin (5-HT), its major catabolic metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and norepinephrine (NE) in chick spinal cord before, during, and after hatching and also to determine if changes in the levels of these chemicals are directly related to the hatching behavior. The levels of 5-HT, 5-HIAA, and NE were measured by high performance liquid chromatography with electrochemical detection in whole spinal cords of 20-day-old "pre-hatching" embryos, 21-day-old "normal hatching" embryos, 0-day-old "post-hatching" chicks, and 0-day-old "glass egg hatching" chicks. NE was measured but no significant differences were found in NE levels among experimental groups. The concentration of 5-HT was elevated in chick embryo spinal cords during normal hatching compared to pre-hatching embryos and post-hatching chicks. The concentration of 5-HIAA was elevated during and after normal hatching compared to pre-hatching embryos. However, neither 5-HT nor 5-HIAA levels were found to be elevated in chick spinal cords during glass egg hatching compared to pre-hatching embryos or post-hatching chicks. Therefore, there appears to be an activation of the serotonergic system in chick spinal cord related to the specific event of hatching but this activation is not directly related to the movements common to both hatching and glass egg hatching.     

Morphological characteristics of tissue components of different layers of the rat myocardium

The tissue components of the subendocardial, inner and outer intramural layers of the myocardium were examined by morphometry. There was no significant difference in the proportion of cardiomyocytes in the different layers of the myocardium (subendocardium 0.820 +/- 0.007; inner layer 0.713 +/- 0.100; outer intramural layers 0.727 +/- 0.008; subepicardium 0.699 +/- 0.009). The relative surface of cardiomyocytes was maximal in the subepicardium (58.62 +/- 1,18). The magnitudes of the volumetric density and surface of the capillaries decreased from the subepicardial toward the subendocardial layer. The diameter of myocytes in the test layers of the myocardium varied within a wide range.     

Spermatozoa of two Eledone species (Cephalopoda, Octopoda)

Spermatozoa from testes and spermatophores of two octopod species, Eledone cirrhosa and E. moschata, have been investigated by electron microscopy. At the base of the mature sperm acrosome of both species a well developed, periodic, conical structure is present. This structure is strikingly similar to that present in the Octopus sp. acrosome. Also the modalities of formation of such a structure during spermiogenesis show strong similarities between the Octopus and Eledone genera. The resistance to disruption of sperm chromatin of E. cirrhosa and E. moschata after treatments with SDS and mercaptoethanol which are known to dissolve disulfide-bridges, reveals the presence of S-S crosslinks.     

初孵扬子鳄嗅球的超微结构研究

用电镜研究初孵扬子鳄的嗅球⒚嗅球的外颗粒层具有明、暗两种细胞⒚僧帽细胞层细胞排列紧密、规则,细胞之间无任何连接结构⒚内颗粒层见有 ３～５ 个细胞聚集成群,并有个别细胞出现胞质降解现象⒚除内颗粒层部分细胞外,其他各层细胞仍处于较幼稚阶段⒚胶质细胞已发生,外网状层中有薄薄的髓鞘出现⒚突触处于不同的发育阶段,大多为不对称型⒚