Читать книгу The Circle of Knowledge: A Classified, Simplified, Visualized Book of Answers - Various - Страница 249

Mammals constitute the highest class of animal creation, and include Man. They have a hard, bony skeleton and a vertebral column or backbone; warm red blood flows in their veins; they breathe by means of lungs, and suckle their young, which they bring forth alive. Their bodies are generally covered with hair. More than three thousand species of mammals are known.