This book reports on zoological research conducted by the author, a Swiss scientist, during three expeditions to the island of Sumatra, in the late 1800's. It provides a detailed account of the large collections of mammals, birds, reptiles, and insects he gathered during his travels. Special attention is given to mammals of the suborder Anthropoidea, which includes primates, particularly the Orangutan. Discussions of the animals' habitats, distribution, biology, and behavior are presented, along with descriptions of the indigenous people and their interactions with the wildlife around them. The author provides a unique and valuable perspective on the rich biodiversity of Sumatra, further highlighting the environmental challenges faced by the island's extraordinary wildlife in the face of human encroachment on their traditional habitats.