Answer to Question 1
The ectoderm develops into the tissues that are on the outside or near the surface of the animal's body. These include the skin, hair, hooves, and certain endocrine glands that secrete hormones into the bloodstream. This layer also forms the central nervous systemthe brain, spinal cord, and all the nerve branches. A group of endodermis cells form a rod-like structure (notochord) that gives rise to the vertebral column. The endoderm forms the digestive system, lungs, liver, and other endocrine glands. The mesoderm layer develops into the skeletal and muscular system of the animal, including bones, muscles, tendons, cartilage, and ligaments. The heart, veins, arteries, and other parts of the circulatory system are also developed in this layer. In addition, the reproductive system is formed from the mesoderm layer.
Answer to Question 2
sand, less than 52 percent; silt, 28 to 50 percent; clay, 7 to 27 percent
An example of layers, or strata, of sedimentary rock that contain fossils
Varicosis. (a) Varicose veins develop due to the failure of valves in the superficial veins of the l
Identify each stage of the life cycle
Testing client’s ability to identify dull sensation
Layers of the heart
Identify the junction nodes in the circuit shown in Figure 21-1.