It is the opinion of the present writer that the theories of Mr. Redfield are in the main true, and that in the future much valuable information will be obtained along the same lines, which will tend to corroborate his general conclusions. One's attention needs but to be plainly directed to the matter, and then he will see that it is absurd to think of a creature transmitting to his offspring qualities which neither he or his mate had inherited or acquired. If there were no transmission of acquired qualities there would be no improvement--and in fact, we know that the bulk of inherited qualities were at some time in the history of the race "acquired." And, reasoning along the same line, we may see that the young parents who have not had as yet an opportunity to acquire mental power cannot expect to transmit it to their offspring--all that they can do is to transmit the inherited stock qualities plus the small acquired power which they have gained in their limited experience. And, finally, it is seen that offspring produced at a riper age of parenthood, continued over several generations, tend toward unusual ability and powers. Consequently, the people or nation with a higher average age of parenthood may logically expect to attain greater mental powers than the peoples lacking that quality. And what is true of a people or nation is of course true of a particular family. The subject touched upon in this part of our book is one of the greatest interest to careful students of Eugenics; and is one which calls for careful and unprejudiced consideration from all persons having the interest of the race at heart. LESSON IX THE DETERMINATION OF SEX The term "The Determination of Sex" is employed in two general senses in scientific circles. The first usage is that of the biologist, and it includes within its scope merely the discovery and understanding of the CAUSES which determine whether the embryo shall develop into a male or into a female. In the discussion of the subject from this standpoint there is but little, if any, attention given to the question of whether the sex of the unborn child may be determined by methods under the control of man. The biologist simply studies the causes which seem to lead to the production of an individual of one or the other sex, without regard to whether these causes, when discovered, may or may not be amendable to human control.