614 FRANCIS M. BALDWIN 



anlage (fig. 19) is composed of numerous large, loosely packed 

 epithelial cells (separated by a light gray matrix), similar in size 

 and shape to the cells of the pharynx with which they are in inti- 

 mate relation. They are surrounded by a thin membrane — a 

 sort of membrana propria — apparently a continuation of that of 

 the upper surface of the pharyngeal wall. It is evident that this 

 body is undergoing degeneration. Maurer found the body on 

 both sides, in an Axolotl 1 cm. long, reduced to two or three yolk- 

 filled cells completely cut off from the pharynx and lying in the 

 connective tissue in about the same relative position as in Ambly- 

 stoma. Maximo w ('12), however, in 10 mm. Siredon larvae 

 found the body still in connection with the pharyngeal epithe- 

 hum, occupying a position ventral to the anterior wall of the ear, 

 between the quadrate anlage and the facial ganglion. ' ^Sie war in 

 einem solchem Fall auf neun aufeinanderfolgenden Schnitten von 

 8 fi Dicke zu sehen und war hier sogar noch mittelst eines diinnen 

 Stiels mit dem Pharynxepithel verbunden." On the other hand, 

 he found the body reduced in 11 mm. larvae, to several irregular 

 epithelial cells completely separated from the pharynx and which 

 occurred in only 2 or 3 serial sections. Driiner, in 11 to 15 mm. 

 stage of Siredon, found the first body still in contact with the 

 pharyngeal cells. 



The second thymus body in 10 mm. larvae is not readily found, 

 as it is reduced to a group of loose epithelial yolk laden cells, 

 situated just cephalad and a little medial to the point where the 

 post-trematic branch of the glossopharyngeal nerve enters the gill 

 arch. These cells, on the right side of the body, are four or five 

 in number and occur in but two successive sections (10 micra 

 each), and are closely applied to the nerve tract. I am unable 

 to find cells corresponding to these on the left side, in 10 mm. lar- 

 vae. In 11 mm. larvae, no trace of the second thymus body is 

 found on either side of the body. 



The third thymus body in 11 mm. larvae (on either side of the 

 body) is free from the pharyngeal entoderm, and lies as a rather 

 compact mass in the connective tissue, dorsal to the cartilage 



