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 i. The 

 medullary folds and notochord are evident at this stage, but no 

 mesoblastic somites are to be seen. 



A sagittal section of approximately this stage, shown in figure ia, 

 represents the foregut, fg, as a shallow enclosure of the anterior 

 region of the entoderm, while the wide blastopore, blp, connects 

 the region of the hindgut with the exterior. No sign of a tail fold 

 being present, there is, of course, no real hindgut. The entoderm, 

 which has the appearance of being thickened because of the fact that 

 the notochord has not yet completely separated from it, is continuous, 

 through the blastopore, with the ectoderm. Posterior to the blas- 



SMiTHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 56, NO. 11 



