ABSTRACT
Without for a moment wishing to underestimate the difficulties in the way, we should like to run over rapidly the arguments which favor the idea of a "thalassal regressive trend", the striving towards the aquatic mode of existence abandoned in primeval times. The word "instinct" or "impulse" or "drive" tends to emphasize rather the factor of adaptation, the purposeful element in organ activiiy; the expression "trend" more the regressive element. In the section on Ontogenesis we spoke of an original similarly directed striving on the part of both the male and the female to penetrate into the body of the sexual partner. The impeding of excretion by the obstructing of the cloaca by the penis and its again becoming free of such obstruction upon the termination of coitus may have led to pleasurable sensations in which the female was able to find a substitutive solace.
