An embryo is an early stage of development of a multicellular organism. In general, in organisms that reproduce sexually, embryonic development refers to the portion of the life cycle that begins just after fertilization and continues through the formation of body structures, such as tissues and organs; each embryo starts development as a single cell resulting from the fusion of gametes. In the first stages of embryonic development, a single-celled zygote undergoes many rapid cell divisions, called cleavage, to form a blastula, which looks similar to a ball of cells. Next, the cells in a blastula-stage embryo start rearranging themselves into layers in a process called gastrulation; these layers will each give rise to different parts of the developing multicellular organism, such as the nervous system, connective tissue, organs. A newly developing human is referred to as an embryo until the ninth week after conception, when it is referred to as a fetus. In other multicellular organisms, the word “embryo” can be used more broadly to any early developmental or life cycle stage prior to birth or hatching.
First attested in English in the mid-14c. The word embryon itself from Greek ἔμβρυον, lit. "young one", the neuter of ἔμβρυος, lit. "growing in", from ἐν, "in" and βρύω, "swell, be full". In animals, fertilization begins the process of embryonic development with the creation of a zygote, a single cell resulting from the fusion of gametes; the development of a zygote into a multicellular embryo proceeds through a series of recognizable stages divided into cleavage, blastula and organogenesis. Cleavage is the period of rapid mitotic cell divisions. During cleavage, the overall size of the embryo does not change, but the size of individual cells decrease as they divide to increase the total number of cells. Cleavage results in a blastula. Depending on the species, a blastula stage embryo can appear as a ball of cells on top of yolk, or as a hollow sphere of cells surrounding a middle cavity; the embryo’s cells continue to divide and increase in number, while molecules within the cells such as RNAs and proteins promote key developmental processes such as gene expression, cell fate specification, polarity.
Gastrulation is the next phase of embryonic development, involves the development of two or more layers of cells. Animals that form two layers are called diploblastic, those that form three are called triploblastic. During gastrulation of triploblastic animals, the three germinal layers that form are called the ectoderm and endoderm. All tissues and organs of a mature animal can trace their origin back to one of these layers. For example, the ectoderm will give rise to the skin epidermis and the nervous system, the mesoderm will give rise to the vascular system, muscles and connective tissues, the endoderm will give rise to organs of the digestive system and epithelium of the digestive system and respiratory system. Many visible changes in embryonic structure happen throughout gastrulation as the cells that make up the different germ layers migrate and cause the round embryo to fold or invaginate into a cup-like appearance. Past gastrulation, an embryo continues to develop into a mature multicellular organism by forming structures necessary for life outside of the womb or egg.
As the name suggests, organogenesis is the stage of embryonic development. During organogenesis and cellular interactions prompt certain populations of cells from the different germ layers to differentiate into organ-specific cell types. For example, in neurogenesis, a subpopulation of cells from the ectoderm segregate from other cells and further specialize to become the brain, spinal cord, or peripheral nerves; the embryonic period varies from species to species. In human development, the term fetus is used instead of embryo after the ninth week after conception, whereas in zebrafish, embryonic development is considered finished when a bone called the cleithrum becomes visible. In animals that hatch from an egg, such as birds, a young animal is no longer referred to as an embryo once it has hatched. In vivaparous animals, the offspring is referred to as an embryo while inside of the parent, is no longer considered an embryo after birth or exit from the parent. However, the extent of development and growth accomplished while inside of an egg or parent varies from species to species, so much so that the processes that take place after hatching or birth in one species may take place well before those events in another.
Therefore, according to one textbook, it is common for scientists interpret the scope of embryology broadly as the study of the development of animals. Flowering plants create embryos after the fertilization of a haploid ovule by pollen; the DNA from the ovule and pollen combine to form a diploid, single-cell zygote that will develop into an embryo. The zygote, which will divide multiple times as it progresses throughout embryonic development, is one part of a seed. Other seed components include the endosperm, tissue rich in nutrients that will help support the growing plant embryo, the seed coat, a protective outer covering; the first cell division of a zygote is asymmetric, resulting in an embryo with one small cell and one large cell (the
GemStone IV is a multiplayer text-based online role-playing video game produced by Simutronics. Players control characters in a High Fantasy game world named "Elanthia"; the first playable version of the game was known as GemStone ][" to "III" maintained significant portions of the environment, but not all, character records were not maintained over the transition, requiring all players to begin anew. GemStone III evolved into GemStone IV in November 2003, but the game world and character records were maintained over the transition. GemStone III was promoted on GEnie by promising players the opportunity to receive real-life versions of gems found in-game, something that persisted for many years. GemStone operated with a license to use the Rolemaster game mechanics and Shadow World environment from Iron Crown Enterprises. In 1995, Simutronics and ICE agreed to let the business relationship expire, necessitating the removal of all ICE intellectual property from GemStone. Many of the game changes were renaming ICE names, such as changing the world name from Kulthea to Elanthia, renaming the deities while keeping their previous characteristics.
Game mechanics were changed with the de-ICEing, which required every game character to undergo significant changes. Character racial and class choices were changed, making any direct translation between the two systems difficult; the end result was that every character was required to "re-roll" their character with the option to change race and skills, but maintaining their old experience level and equipment. GemStone became available on AOL in 1995, just after the de-ICEing process, it had become available on CompuServe and Prodigy before that. When AOL switched to flat-rate pricing, GemStone did over 1.4 million customer-hours in a single month and was attracting 2,000-2,500 simultaneous players. Simutronics launched a web portal in 1997, started phasing customers off of the online services and onto the web interface, although it would take several years before the last of the online service portals were closed. Computer Gaming World in 1991 stated that Gemstone III was a good example of the best and worst aspects of online play.
The reviewer liked the game's community aspect and well-written prose, but criticized the poor parser, "surprisingly empty" game environment and—given the per-minute charge—lack of a free tutorial, concluded that "the present incarnation of on-line games doesn't quite work for him". In a follow-up 1993 review, the reviewer stated "This time, my sojourn in Kulthea was a rewarding experience", he reported receiving help from both built-in commands and other characters and the ability and opportunity for his bard character to sing. The reviewer concluded that "at last, I know why" the game was so popular. In 1997 Next Generation named it as number seven on their "Top 10 Online Game Picks", remarking, "It has depth and racks up 500,000 hours of use a month. Someone must like this game." 1998 Finalist, Online Game of the Year, Academy of Interactive Arts and Sciences December 1996, AOL Members' Choice Award In May 2010, GemStone IV - Shattered was released by Simutronics. It has no policy against automated play.
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The humanist and theologian Jacob Ziegler of Landau in Bavaria, was an itinerant scholar of geography and cartographer, who lived a wandering life in Europe. He studied at the University of Ingolstadt spent some time at the court of Pope Leo X before he converted to Protestantism. For a time he taught at Vienna, his portrait by Wolf Huber, executed about 1540, when he was about seventy years old, is in the Kunsthistorisches Museum, Vienna. His main geographical treatise, was published under the title Quae intus continentur Syria, Arabia, Schondia, Holmiae... at Strasbourg in 1532