Produced by Louise Hope, Mark C. Orton, Linda McKeown and the Online Distributed Proofreading Team at http://www.pgdp.net [Transcriber's Note: Superscript numbers are shown by ^. A few minor printing errors are listed at the end of the text.] Smithsonian Miscellaneous Collections Volume 56 Number 11 DEVELOPMENT OF THE DIGESTIVE CANAL OF THE AMERICAN ALLIGATOR With Fifteen Plates By ALBERT M. REESE Professor of Zoology, West Virginia University [Illustration: Smithsonian symbol] (Publication 1946) City of Washington Published by the Smithsonian Institution 1910 The Lord Baltimore Press BALTIMORE, MD., U. S. A. DEVELOPMENT OF THE DIGESTIVE CANAL OF THE AMERICAN ALLIGATOR By ALBERT M. REESE Professor of Zoology, West Virginia University In a previous paper (6) the writer described the general features in the development of the American Alligator; and in other papers special features were taken up in more detail. In the present paper the development of the enteron is described in detail, but the derivatives of the digestive tract (liver, pancreas, lungs, etc.) are mentioned only incidentally; the development of these latter structures may be described in a later paper. No detailed description of the histological changes taking place during development has been attempted, though a brief description of the histology is given for each stage discussed. The material upon which this work was done is the same as that used for the preceding researches. It was collected by the author in central Florida and southern Georgia by means of a grant from the Smithsonian Institution, for which assistance acknowledgment is herewith gratefully made. Various methods of fixation were employed in preserving the material. In practically all cases the embryos were stained in toto with Borax Carmine and on the slide with Lyon's Blue. Transverse, sagittal, and horizontal sections were cut, their thickness varying from five to thirty microns, depending upon the size of the embryos. The first indication of the formation of the enteron is seen in the very early embryo shown, from the dorsal aspect, in figure 1. The medullary folds and notochord are evident at this stage, but no mesoblastic somites are to be seen.