means of giving us perfectly clear plastic conceptions of the arrangement of parts. The very ingenious wax-plate method was invented by the late Gustav Born, who conceived the happy idea of making wax models of single sections or parts of sections equally magnified in all three dimensions. It is only necessary to pile such wax plates in order, one on top of another, to get a correct model of the whole object. The method is very widely used and in my laboratory, for example, has been employed recently by Dr. John L. Bremer to model the anatomy of a human embryo and by Dr. John Warren to model the developing brain. Such models are truly revelations to one who has studied sections only.
This is not a suitable occasion to review the history of the technical progress of embryological science. I wish only to so far indicate it as may suffice to direct your attention to the dominant importance of method in scientific problems. It seems to me that the greater part of the advance which is made from time to time in modern science is the direct result of either an improvement of old methods or the invention of novel methods. I can see in my own science clearly that this has been the case, and from what I learn about other sciences, infer that it is equally true of them. Viewed from the psychological standpoint, the vast majority of methods have a common purpose, namely, to present the results to the eye, so that we can see what the facts are with which we wish to become acquainted. When we make sections, it is in order to see the cells in their natural relative positions, and with all their various characteristics. When we stain sections, it is in order to make things visible which were before indistinct or perhaps invisible. When we make reconstruction or models it is to furnish again an image to the eye which we can not get from the actual object itself. The eye, indeed, is the chief agent in collecting information for us from the objects by which we are surrounded. It is because they help out the eye that the microscope and telescope have counted for so much. The eye is almost the monarch of research, and reigns even more supremely over our relations with our surroundings than does the ear over our intercourse with our fellow men.
The results of embryology for a long time remained rather meager, and when as a young man I went to pursue some of my scientific studies in Germany, the principal text-book of the science was a modest octavo volume by Professor Kölliker. Since that time (1873) the activity in this domain has increased by leaps, and is now enormous, and the latest handbook of the science, that which is in course of publication at this time under the editorship of Professor Hertwig of Berlin, will comprise eight volumes, each of which promises to exceed a thousand pages when complete; yet the work is only a digest of the researches upon the development of vertebrates and does not
