THE MARINE BIOLOGICAL LABORATORY. 611 



is given up, the pupil is constantly under the eye of the in- 

 structor, 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 ; ho- 

 mology is lacking. In these examples the distinctions are evi- 

 dent, 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 dis- 

 section 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 in- 

 vestigation. 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, 



