The Massive Testicles of Right Whales.

The North Atlantic right whale has the largest testicles in the animal kingdom, weighing around 450-500 kg each when fully grown, which is about the same as a Volkswagen Beetle. However, their testicles are concealed within their body due to the temperature of the ocean water. The whales produce 4.5 liters of sperm, which is a means of "flushing out" the competition during copulation. Older male whales are more likely to successfully breed, which complicates conservation efforts and reduces genetic diversity in whale populations.