formed were arranging themselves in layers and building up the embryo. Such scenes as these have a fascination beyond description, and the student can not repress the feeling that, could he wait a little longer, or were his microscope a little more powerful, he could actually see the force that accomplished these marvelous results. On the morrow, when he returns to his study, the feeling is the same, and no matter if he be witnessing some phase of development, even for the hundredth time, he is as interested as at first. At such times it seems as if the solution to the great problem, "What is life?" were really close at hand.
So far it has been an easy task to describe the process of conversion of an untrained person into an original investigator, but there is another side—a psychological one—which baffles description. All that is necessary in order to perform the various operations which have been thus briefly outlined are power of observation and skill in manipulation; but the facts thus gained must be interpreted in order to render them of real value. A paper which merely details the facts observed of course has its value; but if it adds a comparison of them with the phenomena which occur in other forms, and tells or even suggests their meaning, it then takes a far higher rank. This, however, takes thought, and who can describe the way in which one thinks?
The student tries to master every fact in the development of his embryos, and then compares these facts with what was already known of the development of other forms. In this way he recognizes similarities and differences, for both of which explanations are to be sought. Even in the development of the specimen studied there are many phenomena which have their own meaning, and which, properly interpreted, throw much light on its ancestry and line of descent. In general terms this interpretation is effected by framing an hypothesis which will embrace some of the facts, and then testing it in every conceivable manner. When an objection arises, the first step is to see if it really be founded on fact, or upon a misconception, and then, if it be valid, the attempt is made to reconcile it with the hypothesis. It frequently happens that several hypotheses are formulated before a satisfactory one is found.
Such in brief outline is the training, or rather a part of the training, which is necessary to make a naturalist to-day. The time is past when one can collect a few bugs or shells and then straightway proceed to describe so many new species. Description of species is a necessary work, but it is not the highest kind of work. Far more important, far more ennobling, far more interesting are the deeper problems of how an animal grows, why it grows in the way it does. The training necessary for work of this character requires as long a time, as much patience, and as much perseverance as does any of the so-called learned professions; but when one becomes an original investigator there is no respite. It means continual work, continual study. If one stop,
