Page:Popular Science Monthly Volume 41.djvu/629

Rh is given up, the pupil is constantly under the eye of the instructor, who endeavors to teach him how to use the microscope and its accessories, how to dissect, and, most important of all, how to interpret what he sees. From the animals studied, the young naturalist obtains a broad knowledge of the general structure which occurs in the greater groups of the animal and vegetable worlds, which can be used as a basis for comparison in future work. In giving the necessary instruction, those in charge are continually trying to impress upon the student the necessity of accuracy and the love of truth, and to give him a clear idea of the great principle of homology, which is the very center and soul of modern morphological work.

A word or two may be necessary to explain exactly what this means. Two organs are said to be homologous when they have the same general structure, no matter how diverse may be the uses to which they are put. Thus, for example, if we dissect the arm of a man and the wing of a chicken, we shall find in each similar bones, muscles, blood-vessels, and nerves; in short, a broadly identical structure—they are homologous organs, and yet how different are their functions! On the other hand, when we study the wing of a butterfly or of a bee, we find in it no bones, no muscles, no nerves; and yet it, like the wing of a bird, is an organ of flight. The resemblances are those of analogy; homology is lacking. In these examples the distinctions are evident, but this is not always the case, yet the principle is equally important in all.

These elementary students occupy the ground-floor of the laboratory. Each has his regular seat at the laboratory tables, a locker for his instruments, and his set of reagents and supplies. In the center of the room are the aquaria, where animals for dissection and study are kept. Here he may work "from early dawn to dewy eve," and later if he (or she) desire.

The second floor is dedicated to investigation, and the students here may be divided into two groups. In the first are those who have pursued a course of study essentially equivalent to that of the pupils on the lower floor, and who wish to begin original investigation. It is not an easy problem for the beginner to find out what questions are important to be solved, and even less easy is it for him to attempt their solution. He needs assistance at first at almost every step. For such persons twenty places are provided. The instructors in charge select some problem which needs solution, and which, at the same time, is not too difficult for the beginner, and which, further, will give experience in technique and method of study. They map out the investigation, and watch the embryo investigator in his struggles. Every step in its solution is accompanied with criticism or suggestion, and,