The reproductive system, embryonic development, larval development and metamorphosis of the sea urchin Heliocidaris erythrogramma (Val.) (Echinoidea : Echinometridae)

1975 ◽  
Vol 23 (3) ◽  
pp. 371 ◽  
Author(s):  
DHC Williams ◽  
DT Anderson
Keyword(s):  
Sea Urchin ◽  
Reproductive System ◽  
Water Surface ◽  
Yolk Mass ◽  
Annual Reproductive Cycle ◽  
Juvenile Form ◽  
Pass Through ◽  
Five Phases ◽  
Lecithotrophic Development ◽  
Coelomic Cavities

H. erythrogramma has an annual reproductive cycle, spawning asynchronously. The female cycle has five phases: resting, regenerating, mature, spent and regressing; the male cycle omits the regression phase. Regression and resting occur only during April-August; regeneration begins in September; during December-March individual urchins pass through the mature, spent and regenerating phases two or three times. The egg averages 400 �m diameter and floats at the water surface. At 24-25�C, equal, total, radial cleavage yields a wrinkled coeloblastula by 6-7 hours; this undergoes egression, becoming a spherical stereoblastula by 13-14 hours; during this process an acellular central yolk mass is segregated from a peripheral columnar blastoderm. The ciliated stereoblastula gastrulates by a typical diphasic invagination, beginning at 15 hours, and the gastrulating embryo hatches as a ciliated, planktonic yolk-larva at 15-16 hours. Lecithotrophic development of the yolk-larva to a uniformly ciliated, planktonic vitellaria is complete by 1.5 days, and the larva metamorphoses gradually to a lecithotrophic juvenile over the next 3.5 days. It remains planktonic during the first half of this period (to 3.75 days), but settles during the second half (to 5 days). The juvenile begins to feed >3 weeks after settling. Vegetally proliferating mesenchyme invades the yolk mass during gastrulation. Invagination of the archenteron is followed by evagination of a primary pair of coelomic pouches from its wall; the left enterocoel forms the hydrocoel. Other coelomic cavities are re-formed by schizocoely. The larval gut rudiment temporarily loses connection with the exterior after the blastopore closes. The proctodaeum and stomodaeum of the juvenile form secondarily during and after metamorphosis. Ectodermal development of the echinus rudiment, though gradual, is typical of echinoids. The blastulation of H. evythrogramma is unique among large-egged echinoderms in combining egression of a wrinkled coeloblastula with segregation of a blastoderm around a central yolk mass. The development of the species supports the view that the vitellaria larva is secondarily evolved within the Echinoidea.

A comparative study of the reproductive system of mature, immature and ‘unisexual’ female Schistosoma mansoni

Parasitology ◽  
1973 ◽  
Vol 67 (2) ◽  
pp. 165-183 ◽  
Author(s):  
David A. Erasmus
Keyword(s):  
Comparative Study ◽  
Schistosoma Mansoni ◽  
Reproductive System ◽  
Gland Cell ◽  
Female Worm ◽  
Cortical Granules ◽  
Posterior Portion ◽  
Vitelline Duct ◽  
Vitelline Cells ◽  
Pass Through

The ultrastructure of the reproductive system of mature (54-day-old), immature (32-day-old) and females from unisexual infections of Schistosoma mansoni is described in detail. The uterus is tegumentary in structure but the vitelline duct and oviduct are complex and possess cilia as well as lamellae on their luminal surfaces. The characteristics of the cells forming the walls of the ducts suggests that they may have a digestive function. The posterior portion of the oviduct of the adult worm contains sperm which become enveloped by lamellae. The vitelline cells of the adult contain vitelline droplets, much lipid and little glycogen. A second type of body derived from endoplasmic whorls is also present. Mehlis's gland contains only one type of gland cell and these cells pass through the ootype wall and open into its lumen. The female from unisexual infections has an incompletely developed Mehlis's gland, an ovary in which the Golgi complexes do not produce typical cortical granules and has vitelline cells which remain immature. The oviduct, ootype and uterus are well developed in contrast to the vitelline duct. A comparison with young, but not inseminated worms, suggests that the presence of sperm in the oviduct is not the major stimulus which induces maturation of the female worm.

scholarly journals Ciclos políticos hegemónicos: implicaciones para la gobernanza internacional

2018 ◽  
Vol 7 (3) ◽  
pp. 452-493
Author(s):  
Daniel Morales Ruvalcaba
Keyword(s):  
International Relations ◽  
International Governance ◽  
Political Cycles ◽  
National Power ◽  
Pass Through ◽  
Ideological Transition ◽  
Five Phases ◽  
Power Needs ◽  
International Behavior ◽  
Made In

El hegemón es un actor fundamental en la gobernanza internacional. No obstante, mientras que el comercio, poder y guerra han sido temas ampliamente abordados desde los estudios sobre hegemonía en las Relaciones Internacionales, se ha avanzado poco en análisis de las ideas que orientan el comportamiento del hegemón. La hipótesis aquí planteada es que las hegemonías recorren a lo largo de su existencia cinco fases (emergencia, despliegue, apogeo, declive y extinción) y, durante cada una de ellas, el Estado hegemónico asume ideologías específicas que orientan su comportamiento internacional, lo cual se traduce en la promoción de ciertas políticas internacionales, así como de alianzas y organizaciones internacionales con vocaciones específicas. Sin embargo, en la medida que evoluciona su poder nacional y el hegemón transita de una fase a otra, éste tiende a cambiar ideológicamente, abandonando ideas previas y asumiendo otras nuevas. Si bien dicha transición ideológica es pragmática -en función de las necesidades de su poder nacional- este cambio resulta discordante y criticable por otros actores del sistema. Este documento se compone de dos grandes partes: en la primera se establecen las cinco fases de un ciclo hegemónico y, luego, se exponen las ideologías que orientan el comportamiento del Estado hegemónico en ellas; la segunda parte se orienta a comprobar empíricamente las transiciones ideológicas durante las hegemonías neerlandesa, británica y estadounidense.   Abstract: The hegemon is a fundamental actor in international governance. However, while trade, power and war have been topics widely discussed from studies on hegemony in International Relations, little progress has been made in analyzing the ideas that guide the behavior of the hegemon. The hypothesis proposed here is that the hegemonies pass through five phases during their existence (emergence, deployment, apogee, decline and extinction) and, during each of them, the hegemonic State assumes specific ideologies that guide its international behavior. However, as the national power evolves, and the hegemon moves from one phase to another, it tends to change ideologically, abandoning previous ideas and assuming new ones. Although this ideological transition is pragmatic - depending on the power needs of the hegemon- this change results discordant and is criticized by other actors in the system. To demonstrate this, the following document is composed of two major parts: the first presents the five phases of a hegemonic cycle and, along with it, the ideologies that guide the behavior of the hegemonic State; the second part aims to empirically verify the ideological transitions during the hegemonies that have existed: the Dutch, the British and the American. Keywords: Hegemony, hegemonic political cycles, ideology, national power, hegemonic interregnum.     Recebido em: Agosto/2018. Aprovado em: Dezembro/2018.       

Immune and reproductive system impairment in adult sea urchin exposed to nanosized ZnO via food

2017 ◽  
Vol 599-600 ◽  
pp. 9-13 ◽  
Author(s):  
Sonia Manzo ◽  
Simona Schiavo ◽  
Maria Oliviero ◽  
Alfonso Toscano ◽  
Martina Ciaravolo ◽  
...  
Keyword(s):  
Sea Urchin ◽  
Reproductive System ◽  
Nanosized Zno

scholarly journals Microdissection Experiments on Sea-Urchin Eggs at Cleavage

1953 ◽  
Vol 30 (4) ◽  
pp. 515-524
Author(s):  
J. M. MITCHISON
Keyword(s):  
Internal Pressure ◽  
Sea Urchin ◽  
Sea Water ◽  
Sea Urchins ◽  
The Other ◽  
Membrane Tension ◽  
Membrane Theory ◽  
Sea Urchin Egg ◽  
Pass Through ◽  
Irreparable Damage

1. Chambers (1938) described an experiment in which he cut open one blasto-mere of a cleaving sea-urchin egg at the dumb-bell stage in isotonic KCl. The other blastomere contracted like a ‘deflating balloon’, and this has been taken by other workers as evidence of a positive membrane tension in the cleaving egg. This experiment has been repeated with other sea urchins in various media. It is concluded that this effect only takes place in one species of sea urchin, in an abnormal medium, and after it has suffered irreparable damage. It is not, therefore, legitimate to suppose that there is normally a positive membrane tension in a cleaving egg. It is found that eggs will continue to cleave with one blastomere in an irregular shape which indicates that, on the contrary, there is no membrane tension and no internal pressure. These are the conditions demanded by the ‘expanding membrane’ theory of cleavage. 2. It is found that the furrow of a cleaving egg will pass through a needle placed in its path. This result argues against a simple contracting ring in the furrow region being responsible for cleavage. 3. Chambers (1938) found that an egg will continue to cleave when its asters have been destroyed by stirring. This result has been confirmed by a similar experiment on a different species of sea urchin. This is crucial evidence against an astral mechanism of cleavage. 4. The effects of compressing cleaving eggs have been studied. It is found that compressed eggs continue to cleave unless the degree of flattening is considerable; that cleavage is delayed before it is finally stopped; and that eggs in Ca-free sea water are more susceptible to compression than eggs in ordinary sea water. These results are consistent with the ‘expanding membrane’ theory.

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