The Emperor Shō­wa (also known outside Japan by his personal name, Hirohito) held a great interest in marine biology. He maintained a laboratory at the Imperial Palace in Tokyo and when visiting his villa at Hayama, ensured he made trips to the coast, where he collected specimens from Sagami Bay. Over the course of his life, the emperor collected and described over a hundred species new to science. This book on opisthobranches, a now informal name for a large group of marine gastropods, contains descriptions and illustrations from specimens in the emperor’s own collection.
The illustrations were made by two of the emperor’s assistants, Hiroo Sanada and Shiro Kato and the text edited by Hirotaro Hattori. Hattori was a noted biologist who served as the director of the imperial laboratory. He accompanied Hirohito on his expeditions to Sagami Bay and wrote to fellow naturalists on his behalf.