What Are Ovoviviparous Animals

The term viviparity simply means live birth. Ovoviviparity can be considered a subset of the larger classification—although, the term ovoviviparity (also known as aplacental viviparity) is largely being struck from use since many feel its not as clearly defined as the term histotrophic viviparity. In cases of pure histotrophy, a developing embryo receives nutrition from its mothers uterine secretions (histotroph), however, depending on species, ovoviviparous offspring can be nourished by one of several sources including unfertilized egg yolks or cannibalizing their siblings. Internal Fertilization and Incubation In ovoviviparous animals, egg fertilization takes place internally, usually as a result of copulation. For example, a male shark inserts his clasper into the female and releases sperm. The eggs are fertilized while they are in the oviducts and continue their development there. (In the case of guppies, females can store extra sperm and can use it to fertilize eggs for up to eight months.) When the eggs hatch, the young remain in the females oviducts and continue to develop until theyre mature enough to be born and survive in the outside environment. Ovoviviparity vs. Oviparity and Mammal Development Its important to distinguish between live-bearing animals that have placentas—which includes most species of mammals—and those that do not. Ovoviviparity is distinct from oviparity (egg-laying). In oviparity, the eggs may or may not be fertilized internally, but they are laid and rely on the yolk sac for nourishment until they hatch. Certain species of sharks (such as the basking shark), as well as guppies and other fish, snakes, and insects are ovoviviparous, and its the only form of reproduction for rays. Ovoviviparous animals produce eggs, but instead of laying them, the eggs develop and hatch inside the mothers body and remain there for a time. Ovoviviparous offspring are first nourished by yolk from their egg sac. After hatching, they remain inside their mothers bodies, where they continue to mature. Ovoviviparous animals do not have umbilical cords that attach embryos to their mothers, nor do they have placenta with which to provide food, oxygen, and waste exchange. Some ovoviviparous species, however—such as sharks and rays—do provide a gas exchange with developing eggs inside the womb. In such cases, the egg sac is extremely thin or is simply a membrane. When their development is complete, the young are born live. Ovoviviparous Birth By delaying birth after hatching, the offspring are more capable of feeding and defending themselves when born. They enter the environment in a more advanced stage of development than oviparous young. They can be of a larger size than similar animals that hatch from eggs. This is also true of viviparous species. In the case of the garter snake, young are born still enclosed in an amniotic sac, however, they escape it quickly. For insects, young may be born as larvae when theyre able to hatch more rapidly, or they may be born at a later stage of development. The number of young ovoviviparous mothers give birth to at a given time depends on the species. Basking sharks, for example, give birth to one or two live young, while a female guppy can drop up to 200 babies (known as fry) over the course of several hours.

The Mist Review - 942 Words

The apocalypse is a common subject addressed in films and such Doomsday scenarios have become increasingly popular since the beginning of the Cold War. These films provide a different cause for the downfall of human kind and approach the subject with various degrees of despair and hope. Despite the obvious differences in approach that different directors take, these films all serve to highlight not only the negative qualities of human kind that led to and are represented by the agent of destruction but also to highlight the strength of the survivors who keep the will to fight for their lives despite the bleak circumstances. For the most part, The Mist, adapted from a Stephen King novella, sticks closely to the archetype. The Mist, a†¦show more content†¦The subtle score of Mark Isham is utilized infrequently, magnifying its effect on the particular scenes it is present in. In one of the most suspenseful scenes, a volunteer ties a rope around his waist and ventures into the u nknown. Darabont stays fixed in the store and lets the pull on the rope tell the story, creating great suspense. When the monsters do reveal themselves, the CGI work is seamless and properly horrifying. The question of where they come from or why they have come is never addressed even in the slightest. Darabonts focus is always squarely on the humans, who quickly splinter into competing factions reflecting their own racial, class and educational prejudices. The Mist is as misanthropic as it can get. As most good monster movies, this movie is not about the monsters. The monsters are simply primal fears materialized. The main focus is really the human reaction to the threat. The mist works as a fog of fear, and the store becomes a sample of most kinds of humans from highly educated to low-level working class. The fog becomes the unknown which is unknown to all walks of life. The Mist shows human nature at it worst in a crisis. 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The True Test free essay sample

I traveled 95 miles in 12days in the New Mexico wilderness with a 55 pound backpack on my back. I was in charge. Last summer, I went with a contingent of three fellow scouters and two adult advisors to Philmont Scout Ranch in Cimarron, New Mexico, for a two week adventure. Before the trip, I was elected to be crew leader because I am an Eagle Scout. I have scouted since first grade and demonstrated the leadership qualities needed for this adventure. Throughout the trip, my leadership skills were tested. A fellow scouter in our sister crew got hit in the head with a huge stick and needed stitches. The incident happened when our sister crew was playing a game. As soon as I saw what happened, I rushed over to the injured scouter and organized a group to help get him down to the health lodge. He was okay a day later and rejoined us. We will write a custom essay sample on The True Test or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page After being with the same people for over a week, some of the crew was annoyed by what was done or said. It was my job to make sure this never happened and I was successful. In one case, I convinced a scout he would be safer putting his food covered shirt in the bear bag. After he agreed, he was allowed back in his tent after being pushed out by his tent mates. Never again will I be able to sit on top of a mountain and be able to see for miles in every direction. Never again will I be able to be five feet away from a rattle snake and not be scared or see a United States Air Force Bomber flying inches above the tree line. Or be feet away from a bear that was trying to invade our campsite. Even though I will not be able to experiences these events again, they will live on with me forever. When I first got back, people asked me if I would ever do it again. My original response was no. But after I thought about it, after I thought about how much fun I had, how much I learned, and how much I enjoyed being away from everything, I would have to say I would.