FEEDING REACTIONS IN THE CILIATE, DILEPTVS GIGAS, WITH SPECIAL REFERENCE TO THE FUNCTION OF TRICHOCYSTS. J. PAUL VISSCHER, THE ZOOLOGICAL LABORATORY, 1 THE JOHNS HOPKINS UNIVERSITY. CONTENTS. 1. Introduction 113 2. Material and Methods Il6 3. Experiments on Selection of Food : A. Inanimate Substances I2O B. Animate Substances 123 4. Observations on the Mechanism of Feeding: A. Euglena 126 B. Rotifers 127 C. Colpidium 129 5. Trichocysts : A. Observations on the Nature and the Function of the Trichocysts of Dileftns 132 a. Effect of Trichocysts on Paramecium bursaria 133 b. Effect of Trichocysts on Stentor cocruleus 134 c. Effect of Trichocysts on Paramecium aurelia 136 d. Effect of Trichocysts on Spirostomum 137 B. Observations on the Structure of the Trichocysts in Dilcptns 138 C. Summary of Observations on Trichocysts 140 6. The Mechanism of Selection of Food in Dileptus 140 7. Summary I4 1 8. Literature Cited I4 2 i. INTRODUCTION. Food-getting is the first necessity of the living thing, and the chief end toward which the fundamental structures of the body are directed, and this, whether in the highest mammal or lowest proto-zoan, becomes the chief economic problem to be solved. ' Food-getting, therefore, more than any other function of the body, has been the most influential in leading to morphological development." Thus wrote one of the leading investigators in the field of proto-zoology (Calkins, 5 io). *The work here presented was largely done at the Zoological Laboratory of the Johns Hopkins University, Baltimore. Md., but it has been amplified by work done at the Zoological Laboratory of Washington University, St. Louis, Mo., and at the Marine Biological Laboratory, Woods Hole, Mass. To the directors of these laboratories I am very grateful for facilities offered. 113
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