The extremity of the tail in some American monkeys has been converted into a wonderfully perfect prehensile organ, and serves as a fifth hand.

A reviewer, who agrees with Mr.

Mivart in every detail, remarks on this structure: "It is impossible to believe that in any number of ages the first slight incipient tendency to grasp could preserve the lives of the individuals possessing it, or favour their chance of having and of rearing offspring.

" But there is no necessity for any such belief.

Habit, and this almost implies that some benefit great or small is thus derived, would in all probability suffice for the work.