Zoölogy: The Science of Animal Lifepopular Science Library, Volume XII (of 16), P. F. Collier & Son Company, 1922

A scientific publication written in the early 20th century. The work provides an extensive survey of the entirety of animal life, emphasizing the diversity and complexity of both higher and lower organisms, and highlights the interdependence of different species within ecosystems. It discusses various groups of animals and their classifications while addressing different theories regarding the origin of life. The opening of the text delves into the historical quest to understand life's origin, starting with humanity's attempts to comprehend nature and the evolution of scientific inquiry over the years. Ingersoll outlines the various speculative theories surrounding how life might have begun on Earth, including ideas about meteoric origins and spontaneous generation. He emphasizes the necessity of studying living organisms and their biochemical frameworks to uncover the essence of life, introducing concepts such as cells and the role of chlorophyll in photosynthesis as foundational elements in the relationship between plants and animals. This section establishes a philosophical grounding for the subsequent exploration of animal diversity, bridging scientific thought with the fundamental mysteries of existence.