Yellow Crookneck Squash This is a slightly different cultivar from the straightneck yellow squash, which causes the neck to curve and the skin to get bumpy. This squash tends to be slightly more dense than its cousins, so it can stand up to a bit longer steam, braise, etc.
Their skin must remain moist for them to breathe. Like us, they still need to take in oxygen and expel carbon dioxide. However because they don't have lungs, this process happens though their skin. It's not uncommon to see worms coming to the soil surface after saturating rains. Some hold the view that they suffocate in water saturated soil because there isn't enough oxygen. However worms can survive for some time in water.
They were the first species to develop mesoderm. That mesoderm tissue develops into organs and muscles as the organism grows. They also have simple nervous systems and sensory organs. While they don't have a respiratory system or circulatory system to speak of, they do have a neat little digestive system. Most species of flatworms have no anus and a cavity with only one opening. While not all species do, many flatworm species use a mouth to eat. The only problem with no anus is that the stuff you don't digest has to go out the mouth when you're done. Other materials that need to be removed from the system can be excreted through specialized cells called flame cells. Flame cells are the first appearance of excretory ducts in organisms. Flame.