Complex sentence: After his death, his natural history collection was bought by a group of wealthy men who in 1821 set up the Manchester Natural History Society, and his entomological collection was a central part of the Society's museum.
Split into simpler sentences: After his death, his natural history collection was bought by a group of wealthy men who in 1821 set up the Manchester Natural History Society. His entomological collection became a central part of the Manchester Natural History Society's museum.