THE DEVELOPMENT OF THE' AMERICAN ALLIGATOR 

 (A. MISSISSIPPIENSIS) 



By ALBERT M. REESE 



(With 23 plates) 



Introduction 



With the exception of S. F. Clarke's well-known paper, to which 

 freqnent reference will be made, practically no work has been done 

 upon the development of the American alligator. This is probably 

 due to the great difficulties experienced in obtaining the necessary 

 embryological material. Clarke, some twenty years ago, made three 

 trips to the swamps of Florida in quest of the desired material. The 

 writer has also spent parts of three summers in the southern 

 swamps — once in the Everglades, once among the smaller swamps 

 and lakes of central Florida, and once in the Okefenokee Swamp. 

 For the first of these expeditions he is indebted to the Elizabeth 

 Thompson Science Fund ; but for the more successful trip, when 

 most of the material for this work was collected, he is indebted to 

 the Smithsonian Institution, from which a liberal grant of money to 

 defray the expenses of the expedition was received. 



The writer also desires to express his appreciation of the numerous 

 courtesies that he has received from Dr. Samuel F. Clarke, especially 

 for the loan of several excellent series of sections, from which a 

 number of the earlier stages were drawn. 



The present paper gives a general outline of the whole process of 

 development of the American alligator (A. mississippiensis), it 

 being the intention of the author to take up in detail the more spe- 

 cific points in subsequent researches. 



In preparing the material several kinds of fixation were employed, 

 but the ordinary corrosive sublimate-acetic mixture gave about the 

 most satisfactory results. Ten per cent formalin, Parker's mixture 

 of formalin and alcohol, etc., were also used. In all cases the em- 

 bryos were stained in toto with borax carmine, and in most cases 

 the sections were also stained on the slide with Lyon's blue. This 

 double stain gave excellent results. Transverse, sagittal, and hori- 

 zontal series of sections were made, the youngest embryos being cut 

 into sections five microns thick, the older stages ten microns or 

 more in thickness. 



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