First Final Question.

Roundworm:

Evolution/natural selection:
Roundworms, or Nematodes most likely evolved from the earlier flatworms about 548 million years ago, and like everything else at this time, they lived in the water. Early roundworms had a bi-directional digestive track, meaning that they ingested and excreted the left over food from the mouth. Now roundworms have a unidirectional digestive track where food is taken in from the mouth, digested and absorbed in a long tube and then excreted out the anus.

Characteristics:
feeding/digestion: land dwelling roundworms will eat fungi out of plants, but human dwelling roundworms will feed off of human fluids meanind blood and mucus. Roundworms have a definitive digestive track that runs the length of their body. They do not have a stomach but they have a mouth, phyarinx, intestine, and anus. Because of the lack of a stomach, food id taken directly into the intestines where enzymes are produced.

Reproduction:
All roundworms reproduce sexually. There is a male and a female. The female carries eggs in a oviduct, and the male produces sperm in the testes.

Respiration:
A roundworm has no formal respiratory system. Instead they obtain oxygen and emmit carbon dioxide through diffusion.

Circulation:
A roundworm has no formal blood vessels or heart.

Nervous System:
It has two nerve cords that transmit impulses in the roundworm.

Earthworm

Evolution/Natural Selection:
Worms like all living things began as simple organisms living in aqueous regions.

Feeding/Digestion:
The earthworm has no jaw or teeth so much instead rely on its pharynx . Food enters a long tube where it is stored in the crop, then later the muscular gizzard will ground the food up and it is digested in the instestine. They eat roots of plants, and decaying animals, and most famously, they eat dirt, but only for it's organic matter.

Reproduction:
To reproduce earthworms must mate. They are also hermaphrodites meaning each worm possess male and female reproduction organs. Each worm produces so much mucous that a slime tube forms around their bodies. Each worm then releases sperm into the slime tube and it is then deposited into the other worms sperm recepticales.

Respiration:
Earth worms do not have lungs. Instead they breath through their skin. Oxygen and Carbon dioxide exchange through diffusion.

Circulation:
The earthworm has a closed circulatory system, meaning all the blood is confined to blood vessels and is not floating freeing inside the body.

Nervous System:
The Eathworm has a ventral nerve cord which runs the length of its body and connects to it's brain or cerebral ganglion. Every segment of the earthworms body is connected by segmental ganglion that brach off from the nerve cord.

The Grasshopper.

Evolution/Natural Selection:
Arthropods are the most successful of all living animals in terms of their number of individuals and species, total mass, and complete occupation of terrestrial habitats. Insects seem to be clearly derived from arthropods. Grasshoppers have evolved over time to develope strong enhanced hind legs for jumping and avoiding predators.

Feeding/Digestion
Most grasshoppers are herbivores as they like to eat grass, leaves, and crops, but many grasshoppers are omnivores. Interestingly, many grasshoppers will eat from different plant hosts while some will only eat from one type of plant. Unlike the worm, the grasshopper has a mandible which is able to chew food very slightly, but is the start to mechanical digestion. It has a crop which holds the food and a gizzard to break it down, and a stomach that produces enzymes to break it down and the waste exists through the anus.

Reproduction:
Grasshoppers reproduce sexually. The male introduces sperm to the female through a package into the females ovipositor. They female then inserts the eggs into the ground once they have fertilized.

Respiration:
They breathe through openings on the surface of the abdomen called spiracles where they open to allow for oxygen and carbon dioxide exchange. Help is taken by the use of a tracheae.

Circulation:
Grasshoppers have a open circulatory system where their bodily fluid flow freely filling body cavities and appendages. Its one closed organ is the dorsal vessel which extends the lengh of its body. It is a large tube with two regions: one containing the heart and the other the aorta.

Nervous System:
Has a nerve system controlled by a ganglia, found in all segments of the body and in the head. They have small hairs called sensilla that respond to a certain stimulus.

Starfish

Evolution/Natural Selection:
More than 630 million years ago a revolution within the animal kingdom appeared-the deutrerostomes. Two phylum conprised this group: the echinoderms and the chordates. Over time the starfish has evolved to have the ability reproduce even if it is fragmented.

Feeding/Digestion:
Most starfish are predators and eat sponges, snails, bivalves, and microalgae, but some can be detrivores and feast of decomposing organic material and faecal matter. Starfish use their cardiac stomach which can be everted from its body to engulf and digest its food.

Reproduction:
There is a male and a female starfish and they can reproduce sexually or asexually. Although reproducing asexually will only result in two whole starfish with the same DNA.

Respiration:
The starfish breathes through gas exchange in two areas, one, on the skin at then ends of its tube feet, and the second at the top of their bodies through papulae.

Circulation:
It has three rings of blood vessels. One around the mouth, another around the digestive system and one around the aboral surface. It has radial canals that run through all the arms and join in the middle that functions as a circulatory system.

Nervous System:
Starfish are sensitive to light, touch, temperature, and orientatiom despite having any well defined sensory organs. They are sensitive at their tube feet and have eye spots on the ends of their arms. A starfish had radial nerves running the length of each ray and it has s nerve ring that connects all radial nerves.

Grass Frog

Evolution/Natural Selection
Evidence suggests that frogs date back to 265 million years ago. It is one of the most diverse vertebrate species inhabiting tropic regions to subarctic regions. Most notably frogs have been seen as having adapted to living on land as well as in the water making them amphibians. To adapt to living on land they have developed teeth in order to make predation easier on land.

Feeding/Digestion:
Unlike other animals before it, frogs have an oesophagus that food will travel down to get to the stomach. Digestive enzymes will churn up the food where it will then proceed to the small intestines where the majority of the digestion occurs. To catch prey frogs use their cleft tongues which can be shot out and retracted at great speeds. They eat greens and algae as tadpoles, but when they mature into adults they begin to feed on flies and other insects.

Reproduction:
There are female and male frogs and they reproduce through extermal fertilization. The female lays her eggs in the water and the male swims over to fertilize the egg. These eggs then hatch into tadpoles and will later metamorphasis into adult frogs.

Respiration:
A frog can breathe through its lungs and skin. When submerged in water it can directlty diffuse oxygen into its blood because of the blood vessels located near the surface of its skin.

Circulation:
The frog has a three chambered heart where oxyginated blood and deoxyginated blood enter the heart through seperate atria. When the chambers contract the two seperate blood streams pass into a commen ventricle before the oxygentaed blood is passed into the aorta and the pulmonary artery for deoxyginated blood. The reasons frogs have a higher metabolic rate is because the chance of the two types of blood mixing is very low because the ventricle is partially divided into narrow cavities.

Nervous System:
Unlike the past animals, frogs have a highly developed nervous system with a brain, spinal cord and nerves.A frogs brain can be very similar to that of a humans, it consits of two olfactory lobes, two cerebral hemispheres, a pineal body, two optic lobes, a cerebellum and a medula oblongata. One difference is that the cerebum in frogs is much smaller than in humans.

Growing Complexity:
Now that we can see the similarities and differences between these animals it may be easier to look at them in terms of their complexity. On the simpler side we have round worms. A simple tube digestive track with no real brain, no major organs, and no circulatory system, this animals gets where it needs to be, which would be in your intestines. Slowly we can see small changes as we move up the ladder of species. The earthworm is like the roundworm but add a crop, and gizzard to help it digest food. Then there is the grasshopper, who's insides will looks largely like the earthworm but the organs such as the gizzard, crop and intestines are much more difined, easy to see and larger. There is also the starfish. Unlike the previous animals they have blood vessels and are advanced in the sense thay they can regrow a lost limb and reproduce asexually. Then finally, the large jump between all the animals to the grass frog. The grass hopper unlike the other animals has a brain! It has major organs such as lungs, a heart, a liver, a stomach, and intestines. The frog is independant, and successful in it's environment. You can clearly see the increase in complexity when knowing about these animals. From no brain, to a full brain and from one large organ to humanoid organs, the efects of evolution are clear.