Mori Sosen devoted his work entirely to painting monkeys. He was part of a flourishing art market during the Edo period that was patronized by wealthy merchants and established families, allowing artists to explore a wide range of visual approaches and theories. His style is closest to the Shijo school that was centered in Kyoto, where Sosen was exposed to many different aesthetic movements.
Monkey and Wasp by Mori Sosen • Baby Chimp Sculpture Art Pendant • Monkey Peering Over a Cliff by Watanabe Nangaku
The quality of his brushwork indicates that he was influenced by western realism as well as native traditions. His compositions in particular echo the distinct relationships between empty space and ink in Zen paintings. The variety of gestures and poses of his monkeys suggests that he had a deep understanding of their behavior and sought to convey their personalities.
Well-written essay about finding the inner animal: http://www.pacificasiamuseum.org/japanesepaintings/html/essay2.stm