One should bear in mind how very generally pioneer work of this kind is liable to err. Further, in the _History of Creation_ there is the danger involved in the popular presentation of the results of scientific research. Any man who has written popular works, or delivered lectures to the general public, knows what this means. There is little common measure between them. The truths of science are in a state of constant flux; it is of their essence to be so. To fish out a piece from this stream, fix it, and magnify it for the public with a broad beam of light, really amounts in principle to an alteration of it; it is putting a certain pressure on things, and giving them an arbitrary shape. The work of popularising truths is so holy a thing in its aim that this risk has to be run. We must take things as they are. We have two alternatives: either not to popularise at all, or to take the apparatus with all its defects. We can diminish these according to our skill; but there is a subjective limit to this skill in all of us. The first edition of the _History of Creation_—Haeckel’s first attempt at popularising—had a good deal of inequality in this respect. To begin with, the book had the air of an extempore deliverance. Its success was very largely due to its being cast in this form. But there was a good deal that could be improved here and there, and was improved in the later editions of the work. In the tenth edition, as we now have it, it is a splendid work in regard to the illustrations, for instance. But the first edition was merely provided with a few very crude woodcuts in outline. Some of them were very clumsy. In comparing different embryological objects the same blocks were used sometimes, and this would give rise to misunderstanding in the mind of the reader. For instance, there was question of demonstrating that certain objects, such as the human ovum and the ovum of some of the related higher mammals, were just the same in their external outlines. This fact is quite correct and established to-day. If I draw the outline, and write underneath it that as a type it is applicable to all known ova of the higher mammals, including man, there is no possibility of misunderstanding. But if I print the same illustration three times with the suggestion that they are three different mammal-ova, the general reader is easily apt to think, not only that they are identical in the general scheme of this outline, but also in internal structure. He imagines that the ova of man and the ape are just the same even in their microscopic and chemical features. This leads to a contradiction between the illustration and what Haeckel expressly says in the text. We read that there is indeed an external resemblance in shape between these ova, but that there is bound to be a great difference in internal structure, since an ape is developed from the one and a human being developed from the other. It would have been better if the general reader, who is not