Homology, Analogy and Plasis

IN THE days of Spallanzani and of John Hunter comparative anatomists did not scruple to employ experimental means as an aid to investigation. In their time no hard and fast distinction had been made between questions pertaining to structure and questions pertaining to function. Function and structure being viewed as more or less of a unity, biologists felt free to employ any available means in the investigation of their multifarious problems. In the process of historical development physiology hived off from anatomy and very soon two distinct sciences, each employing its own special technique and animated by its own particular aims, had replaced the more generalised biology of Hunter. During the nineteenth century the separation between them became profound. Of recent years we have witnessed a strong tendency on the part of zoologists and anatomists to recur to the experimental method. It began with Darwin and to a less degree with Milne Edwards. It received a very strong impulse in a special direction from Wilhelm Roux and in another direction from Gregor Mendel. More particularly in America, where a strong group of men, prepared in Johns Hopkins University by the joint labors of Brooks and of Newell Martin, were ready at an opportune moment to develop and greatly to extend the biology of Roux and of Mendel, zoology is now viewed as an experimental rather than as a comparative science. In process of time no doubt matters will readjust themselves and the comparative method of studying structure will again come more into vogue. When it does it too will have to be handled experimentally. As physiologists are not generally aware of the opportunity open to them of participating in some of the classical problems of comparative anatomy, and as the morphology of our fathers has for the moment fallen on evil days, it seemed worth while to go over the history of the original separation between physiology and comparative anatomy with a view to make some constructive attempt towards a rapprochement between them. The whole issue is rather a wide one and cannot well