Mark Sloan’s photographs of items in the collection of the Harvard Museum of Natural History tell only half the story; the rest is voiced in the mind’s eye by a tweedy, slightly daffy scientist. Image: boxes of snail shells. Backstory: Stephen Jay Gould made his career by tracking their variations as he played Darwin in the West Indies. Image: egg of the elephant bird. Backstory: Was deposited by an extinct, ostrich-like creature that stood 11 feet tall. Image: blazingly blue butterfly. Backstory: One half is female, the other half is male. (It was born that way, in a genetic fluke.) Still, the winner for best yarn has to be the one that accompanies the image titled “Nabokov’s Genitalia Cabinet,” which sounds like an English-major’s in-joke. Yes, it’s that Nabokov, and the cabinet, with sagging cardboard shelves, contains samples of butterfly genitalia the novelist collected while toiling at the Harvard Museum of Comparative Zoology in the 1940s. You just can’t make up stuff like that. the EXHIBITION is on view 9 A.M.–5 P.M. MONDAY–FRIDAY TO JAN. 7, AT THE NATIONAL ACADEMY OF SCIENCES, 2101 CONSTITUTION AVE. NW. FREE. (202) 334-2436.