Final Question #1

Digestion:

Roundworm- does not contain stomach but goes from mouth to pharynx to intestines to rectum to anus.

Earthworm- digestion occurs from mouth to pharynx to esophagus to crop to intestines and to anus.

Grasshopper- mouth to pharynx to esophagus to crop to gizzard then to anus.

Starfish- food goes in mouth to stomach to intestine to anus. The stomach comes out of its mouth and releases digestive juices on its pray so it can then eat/absorb the partially digested pray.

Frog- food goes from mouth to pharynx to esophagus to stomach to small intestine to large intestine to anus. 
** digestion path is very similar to humans.

Reproduction:

Roundworm- Have a male and a female. Female goes through internal fertilization.

Earthworm- Hermaphrodites. Go through internal fertilization and form a cocoon at their rear once fertilization occurs. 

Grasshopper- Have a male and a female which reproduce internally. Produces about 10-30 offspring which then later mature like their parents. 

Starfish- Hermaphrodites. Can produce sexually and asexually. Firstly, they can use their gonads to release its reproductive parts (sperm + egg) into the water. It can also cut off an arm with either the eggs or the sperm, and grow another starfish!!!

Frog- Has a male and a female which reproduce externally. They lay their eggs in the water until they eventually hatch and live on land. 

Respiration:

Roundworm- No respiration but releases Carbon Dioxide.

Earthworm- No respiration but breathe through their skin. 

Grasshopper- Have something called Spiracles on their sides that connect to the trachea and exchange Oxygen and carbon dioxide. This is especially important because they do not have lungs.

Starfish- Ampulla helps with respiration but they don`t have lungs. 

Frog- Contain lungs as well as can breathe through the skin. Respiration system is very similar to humans.

Circulation:

Roundworm- None

Earthworm- contain 3 main blood vessels. Dorsal Blood Vessel (brings blood to the front of the body), Ventral Blood Vessel (takes blood to back of body), and Aortic Arches (pumps blood to Ventral and Dorsal Blood Vessels) 

Grasshopper- Contains heart. Blood doesn't flow on its own but rather stays in place. 

Starfish- Uses the Water Vascular System through the Madreporite. 

Frog- Similar to humans- uses heart to pump blood to other arteries/veins. 

Nervous System:

Roundworm- contain Dorsal and Ventral Nerve cord that transmits impulses throughout the body. 

Earthworm- Contains Segmental Ganglions, Celebral Ganglion (brain-like) and a Ventral Nerve chord which help it move. 

Grasshopper- contains brain, eyes, antenna and the Ventral Nerve Chord which helps it move. The brain isn't very important to the grasshopper, but instead the antenna. 

Starfish- Only contains eyespots at the end of each arm. No brain.

Frog- Very similar to humans. Contains a brain which connects to the spinal chord and the rest of the nervous system to help it move and feel things. 

We can easily see how in each of these categories, the species get more and more complex. This could easily be an example of Natural selection. With the explanation I gave for each category,  you can the the characteristics and the ability for one to survive in the environment. Its obvious that the frog is the strongest of all in many ways. Also, I wonder why the frog is so similar to humans. At one look, you would never guess what goes on in that little body of theirs. There are some similarities between the animals listed above. For example, the all have a mouth and an anus. Also, every single one of these creatures contain a Ventral Nerve Chord in their nervous system. Each of these species are so special in their own way and I'm glad I got to learn about them.