THE DEVELOPMENT OF THE LUNGS OF THE 

 ALLIGATOR 



By A. M. REESE 

 west virginia university, morgantown, w. va. 



(With Nine Plates) 



As in the chick, the primordia of the lungs in the alligator are 

 budded off from the ventral side of the pharynx just caudad to the 

 region of the gill clefts. They are first seen in embryos of about 

 thirty somites, slightly younger than the one shown, in outline, in 

 figure i. (The figures are arranged consecutively on plates at end of 

 paper.) 



Figure 7 represents a wax reconstruction of the respiratory tract 

 of an embryo of the stage shown in figure 1. Four gill clefts and 

 about thirty-five somites are present in this embryo ; but the buds 

 of the appendages are not yet visible. The allantois is evident, just 

 anterior to the tail, but the yolk stalk was torn away and hence is 

 not shown in the figure. 



In the embryo from which this reconstruction was made the 

 right bronchial bud was considerably thicker than the left, but ex- 

 tended only about half as far caudad. It is frequently the case that 

 one bronchial bud pushes caudad faster than the other. The planes 

 of the sections are indicated by the numbers 2 to 6, in figure 7. 



Figure 2 represents a section through the pharynx, in the region 

 of the last gill cleft, c, of the stage under discussion. As seen in 

 the figure, the epithelium of the cleft is here continuous with that 

 of the pharynx, though there is no opening at this point. This 

 section is at the anterior end of the deep, median depression, g, in 

 the floor of the pharynx which extends from this point caudad for 

 a considerable distance, and is called by Lillie the laryngo-tracheal 

 groove. This groove is deep, and is so narrow that its cavity is a 

 mere vertical slit; it is open throughout its length to the trachea 

 above. At its posterior end the groove suddenly becomes less deep 

 and widens out, as shown in figures 3 and 7. The plane, 2, of this 

 section is in the region of the extreme anterior end of the recon- 

 struction, figure 7. The lining of all these cavities consists, at this 

 stage, of a compact, stratified epithelium, six or more cells deep. 



Smithsonian Miscellaneous Collections, Vol. 65, No. 2 



