The system that circulates blood through the body, consisting of the heart and blood vessels. In all vertebrates and certain invertebrates, the circulatory system is completely contained within a network of vessels. In vertebrates, the lymphatic system is also considered part of the circulatory system.
While a squirrel isnât going to pen the next bestseller or ace a calculus class, the squirrel is smart in his own way. When looking at animal intelligence, humans shouldnât judge animals by human standards.
Compared to similar-looking rodents like mice and rats, squirrels are incredibly long-lived. The evolution of long life is thought to occur in animal species with low levels of predation,1 and squirrels fit the bill. Since they live in trees and are very quick and agile, squirrels are hard for predators to catch.