Now we have completed what was necessary to arrive at our conclusion of what it is that goes to the making of an embryo, and therefore of a human being--a personality. The conclusion is that every characteristic which it is possible for an individual under any circumstances whatsoever to possess is traceable ultimately to the action which takes place between his inherited tendencies and his natural environment. This environment, whether it be physical, mental, moral, ethical, spiritual, or whatever other can be imagined, can only produce the whole individual by means of acting upon what is already present. To that material nothing can be added _except in the environment_; from that material nothing can be taken away; the most that can be done in this direction is to hinder its growth by suitable procedures. Hence the truth of the phrase that "education is nothing more than the giving or withholding of opportunity." Hence it is so entirely true that it is impossible to make a silk purse out of a sow's ear, or to gather grapes from thorns. The importance of thoroughly realising these simple facts of embryology should at this stage be obvious. They constitute possibly the most important lesson which is demanding attention at the hands of modern teachers, parents, and sociologists. One further word before we leave this part of our subject. It is obvious that of our total characteristics some are acquired and some are inherited, and the question then arises, How much is inherited in an embryo or individual, and therefore unavoidable, and how much acquired? It would be beyond the scope of our subject in this place to enter into detail in this matter, but it would not be right to pass the question by without pointing out that a careful analysis of individual characteristics will show that under the heading of "Inherited" will be found principally the physical traits. When the reader comes to estimate his mental and moral characteristics, a very few moments' careful thought will prove most conclusively to him that these must be entered up under the heading of "Acquired." If it were not so progress in those directions would be practically hopeless. But plain as is this truth, it is one which is far from being realised by many well-educated people. CHAPTER V FERTILISATION AND EARLY DEVELOPMENT