read.Black widow's have 2 kinds of breathing organs-tracheae and book lungs . Tracheae are small tubes which carry air to the body tissues. Air enters the tubes through 1 or, rarely, 2 spiracles. A spiracles is an opening in front of the spinnerets. Book lungs are in cavities in the spider's abdomen. Air enters the cavities through a tiny slit on each side and near the front of the abdomen. Each lung consist of 15 or more thin, flat folds of tissue arranged like the blood vessels. As air circulates between the sheets, oxygen passes into the blood. The blood of black widows contains many pale blood cells and is slightly bluish in color. The heart, a long, slender tube in theabdomen, pumps the blood to all parts of the body. The blood returns to the heart through open passages instead of closed tubes, such as those of the human body. If the spider's skin is broken, the blood quickly drains from its body.A digestive tube extends the length of the spiders body. In the cephalothorax, the tube is larger and forms a sucking stomach. When the stomach's powerful muscles contract, the size of the stomach increases. This causes a strong sucking action that pulls the food through the stomach into the intestine. Juices in the digestive tube break the liquid food into molecules small enough to pass through the walls of the intestine into the blood. The food is then distributed to all parts of the body. Food is also pulled through the stomach into a finger-like cavity called the caeca. The ability to store food in thecaeca enables spiders to go for long periods of time, over a year in some cases, without eating.The central nervous system of the black widow is in the cephalothorax. It includes the brain, which is connected to a large group of nerve cells called the gandlion. Nerve fibers from the brain and gandlion run throughout a spider's body. The nerve fiberscarry information to the brain from sense organs on the head, legs, and other parts of the ...
