Animal reproduction

Ok, sadly, I'm out of ideas for the topic on premarital sex and its consequences, so let us go back to my initial topic, on sexual reproduction. So I will now formulate a third question, describe sexual reproduction in other organisms other than mammals.

So, let us first deal with verterbraes. I will begin with birds. Birds reproduce by sexual reproduction, males having paired testes lying in the bodity cavity, and females having only a functional left ovary and oviduct. Firstly, a stimulus occurs weeks in advance of the breeding season in the birds. This ensures the male arrives on the breeding grounds with the testes fully developed and the female has enlarged of the female reproductive organs, development of eggs in the ovaries, formation of the brood patch, and so on. These enlarged testes secrete greater amounts of male hormones that may brighten skin colors and stimulate singing and courtship behavior.

After mating, copulation occurs, in which the male mounts the female from behind. Both sexes hold their tails to the side and turn back the feathers around the cloaca (the common opening of the bird's alimentary canal and excretory and reproductive systems), so that the swollen lips of the male's and female's cloacae can come into contact. In some birds, such as geese and ducks there is a grooved, erectile penis inside the male's cloaca that guides the sperm, which have been stored in a nearby sac, into the female. In passerines, there is no penis, and copulation amounts to a brief "cloacal kiss" during which the sperm are transferred out of the testis, into the vas deferens and into the female
Once transferred, the sperm remain for a while in storage at the lower end of the oviduct, and then swim to the upper end of that duct to fertilize the egg. Consequently, there is considerable variation among species in the frequency of copulations, how long it takes for the egg to be laid and how many eggs are actually laid. But in order for an egg to form, the sperm must meet the egg in the oviduct before the layers of the egg form.

The birds will be laid in nests that vary from burrows(penguins) to leaf piles(turkeys). When eggs are laid, all birds will incumbate their eggs by supplying heat from their bodies. That heat may be considerable, since the normal temperature of a bird is around 100 to 112 Fahrenheit. Once incubation begins the bird seldom leaves the nest, and then not long, because the eggs will not hatch if they get too cold. During incubation the eggs have to be turned once or twice a day so that they will be heated evenly and the membranes of the embryo will not adhere to the shell.

So now a bit more about a bird egg. The egg cell of a bird is really what we call the yolk. The yolk is the food supply for the developing embryo. The nucleus of the bird's egg can be found in the middle of a white spot which is found on top of the yolk. The egg that female bird lays is covered in layers of albumen (a material like jelly), two membranes and a hard shell. The shell and the membranes protect and support the egg. The albumen feeds the developing embryo with water and protein. The albumen, membranes and shell are added to the yolk layer-by-layer as it passes down a tube called the oviduct inside the hen's body.

When the egg actually hatches, the characteristics again vary species to species. Some hatch naked, while others hatch with their full feathers. Some are blind, others can already move. Thus, there is a lot of difference which makes bird reproduction very fascinating.

I thank www.stanford.edu/group/stanfordbirds/text/essays/Copulation.html, http://www.saburchill.com/chapters/chap0034.html and www.newton.dep.anl.gov/natbltn/400-499/nb456.htm for the info.