644 FRANCIS M. BALDWIN 



das Organ noch den Eindruck eines soliden Epithelschlaliches und erst 

 nach Metamorphose bildet sich ein weites Lumen, das jedoch niemals 

 Colloid enthalt. 



The appearance of a postbranchial body on the right side as 

 well as on the left in this specimen, is unusual, since in none of the 

 other stages or specimens is it present. The fact however, is of 

 interest, for it indicates that the development of this body may 

 vary within a single genus of urodeles, as well as among different 

 families, as has been pointed out by Miss Piatt. 



F. Amblystoma larvae, 26 mm. long. In the 26 mm. stage, the 

 postbranchial body on the left side is a fairly compact structure, 

 little different in position and general appearance from that of the 

 19 mm. larva, but in the subsequent stages, several irregularities 

 may occur. In a wax reconstruction, (fig. 44) it is an irregular, 

 elongate body, rather tapered at the anterior end, and somewhat 

 blunt caudally. On its surface, here and there, are numerous 

 lobules, resembling follicles, but which are unevenly distributed. 

 The cephalic end lies close above the dorsal wall of the peri- 

 cardium between the aditus laryngeus muscle and the cartilage 

 of the fourth branchial arch, and the caudal end is just below the 

 ventral wall of the pharynx. It has a length of about 150 micra, 

 and for the most part it is solid, only here and there do the sec- 

 tions show a lumen. 



G. Amblystoma larvae, 35 to 1^0 mm. long. In larvae 35 mm. 

 long, the body has divided into numerous smaller components 

 which are distributed over a little greater longitudinal area. 

 Portions of it occur in 18 section? (10/x thickness each), so that it 

 is about 180 micra long. The anterior third is follicular, a layer 

 of cuboidal epithelial cells enclosing a fairly large lumen. Behind 

 this is another third, which is oval in shape and solid and is some- 

 what flattened dorso-ventrally, with irregular bud-like groups of 

 cells on its surface. The caudal end has separated into several 

 cell groups, with large lymph spaces and connective tissue be- 

 tween them. The caudal extremity, as before, lies just below the 

 floor of the pharynx, and the cephalic end close to the dorsal wall 

 of the pericardium. 



Driiner's description of the body in 36 mm. stage of Siredon 



