The souls of animals, unlike those of men, are not immortal. The intellect is part of each man’s soul
 Bertrand Russell, A History of Western Philosophy (1945). copy citation

Context

“angels have no bodies, but in men the soul is united to a body. It is the form of the body, as in Aristotle. There are not three souls in man, but only one. The whole soul is present entire in every part of the body. The souls of animals, unlike those of men, are not immortal. The intellect is part of each man’s soul; there is not, as Averroes maintained, only one intellect, in which various men participate. The soul is not transmitted with the semen, but is created afresh with each man. There is, it is true, a, difficulty:” source