From the July 18th New Scientist, in the In Brief section, “Zoologger: The sex-addicted tiny lemur with giant testicles” (on-line; in print, “Tiny lemur is best endowed primate”):
“Oh my god! How do they manage to walk and climb without bumping these things on every branch?” asked Johanna Rode-Margono the first time she saw the testicles of a giant mouse lemur close up.
In turns out they don’t. They stumble and bump their balls with almost every step they take, says Rode-Margono, who is at Oxford Brookes University, UK. At a mere 300 grams, the lemur is roughly squirrel-sized. But for its size, it has the largest testicles in the primate world (American Journal of Physical Anthropology, doi.org/54q).
If we had the same testes size, relative to weight, the average man would have balls as big as grapefruits, says Rode-Margono.
The lemurs mate all year round but constant copulation has not saved them from deforestation – fewer than 17,000 giant mouse lemurs are left, she says.