PHARYNGEAL DERIVATIVES OF AMBLYSTOMA 643 



und liegt als solide Zellkugel direkt unter der Schlundwand, seit- 

 lich vom Kehlkopfeingang." 



E. Amhlystoma larvae, 19 to 20 mm. long. In a single speci- 

 men, 19 mm. long, contrary to the usual condition, two post- 

 branchial structures are developed, one on the right, and the 

 other on the left side of the body. Both have the same general 

 structure, and occur in the same relative position on the two 

 sides, although the right is much smaller. The right body is 

 about 105 micra long, and about 20 micra in average diameter, 

 while the structure on the left is 165 micra long, and nearly 50 

 micra in average diameter. A transverse section through the 

 central portion of the body on the left side is shown in figure 25. 

 Both, for the most part, are compact, but here and there through- 

 out their extent each shows the presence of small cavities, which 

 have the appearance of lumina, but which do not contain colloid. 

 These cavities are not continuous with one another; the}- maj- 

 appear in one section and in the next disappear. 



A wax reconstruction of the postbranchial body of the right 

 side is represented in figure 38. The cephalic end is bent ven- 

 trally, so that it lies close to the dorsal wall of the pericardium, 

 and is insinuated between the lateral surface of the aditus laryn- 

 geus muscle, and the fourth afferent branchial artery, while the 

 caudal extremity is turned slightly in the opposite direction and 

 lies close to the ventral w^all of the pharynx. In addition to a 

 small twig of the fourth afferent branchial artery, which, as men- 

 tioned above passes to the ventral w^all of the pharynx in this 

 region, numerous lymph spaces now occur, which in places nearly 

 envelop the postbranchial body, especially in the region of its 

 caudal extremity. 



Except for the appearance of the body on the right side, as 

 noted above in a single individual, the general position and struc- 

 ture of this body in Amblystoma, at this stage of development, 

 is similar to that recorded by Maurer in Triton, p. 362. 



In den nachsten (second) Wochen wachst dies Gebilde in Lange, be- 

 halt seine Lagerung bei und liegt medial von der Knorpelspange des 

 vierten Kiemenbogens. Sehr friih tritt schon ein feines centrales 

 Lumen darin auf ; indess macht bei alteren Larven, von 2-3 cm. Lange, 



