Limits on Animals and plants Size

The book presents a theory linking the size of organisms to their circulatory systems and the influence of gravity. It explores how the absence of a circulatory system in the smallest animals limits their size, while those with open or semi-open systems, like crustaceans and mollusks, can grow larger. It further explains that larger animals, including mammals, possess a closed circulatory system with advanced structures, such as a four-chambered heart, enabling them to achieve greater bulk. This relationship between structure, gravity, and function is a central theme.