present use, but showing resemblance to organs in other animals which are useful. The appendix vermiformis is one such structure, a mere vestige of an organ of great great importance in some lower mammals. The human tail—bony coccyx with its rudimentary muscles—is another. The wisdom teeth of man are approaching a vestigial condition.
It is interesting to observe that an organ in one kind of animal may have a different use from the similar organ in a related animal. There are very few, if any, structures in man, for example, which do not show clear indications of relationship to, descent from, an organ of different use in some related animal. The lungs of man correspond to the swim bladder of fishes; hair has apparently been derived from tactile sense organs in the skin of aquatic vertebrates; certain bones connected with the human larynx were derived from the supporting arches in the bars between the gill slits of our aquatic ancestors; our teeth were once scales in the skin and so on and so on. Probably there is no structure in the human body which was not at some time used for a different purpose. As the use of an organ changes, in evolution, its structure correspondingly changes and we see most complete series of intergrades between the earlier and the later conditions.
In all this discussion I have not used the word "species." There are no such things as species in nature. In nature we find different kinds of animals and plants. The words "species," "genus" "family," etc., are terms used to describe the fact that animals and plants differ among themselves and differ to different degrees. Those that are closely similar, that is, closely related, we class in one species; those less closely related, but still not too different, we place in different species, putting the related species together in one genus and so on. Species, genera and so forth, are man-made pigeon holes in which to classify the real animals and plants seen in nature. I have recently made about 150 species of protozoa, but I have never made an animal. The word species is indefinable, and is used by biologists merely as a convenience, and it has wholly different meanings when applied to different groups of anmials and plants. There are many genera of animals and plants in which most of all the species completely intergrade so that specific distinctions are purely artificial. This is true to large degree among the protozoan forms I have been studying recently. I have made species among them on the basis of distinctions far too minute to be considered for a moment as of "specific" value among, say insects or mammals.
By Dr. Winterton C. Curtis
Zoologist, University of Missouri.
Biograph—Dr. Winterton C. Curtis received the degree of doctor of philosophy at Johns Hopkins in 1901. He has served the University of Missouri since the latter date, and is now chairman of the department of zoology in this institution. He has also been associated with the Marine Biological laboratory at Woods Hole, Mass., for many years, being at the present time one of its trustees. At various times he has acted as an investigator for the United States Fisheries bureau, notably in studies upon the pearl-button mussels. His numerous technical papers have been along the general lines of invertebrate zoology, regeneration and parasitology. His recent work entitled, "Science and Human Affairs," undertakes a discussion, from the standpoint of biological science, of the relationships between the advancement of scientific knowledge and our civilization. Dr. Curtis is particularly qualified to speak in the matters under consideration, because in this volume he has emphasized the spiritual rather than the material influences of science. He is a member and past secretary of the American Society of Zoologists, of the American Society of Ecologists, the American Naturalists, and a fellow of the American Association for the Advancement of Science.
