Mast's groundbreaking research into the reactions of spirillum hydra and fresh-water planarians to changes in temperature sheds important new light on the behavior of these organisms. Through meticulous experimentation and analysis, he demonstrates the ways in which these creatures can adapt to changing environments or react to potential threats. The book includes detailed scientific data as well as commentary on the broader implications of Mast's work. This work has been selected by scholars as being culturally important, and is part of the knowledge base of civilization as we know it. This work is in the "public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work. Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.