656 FRANCIS M. BALDWIN 



of the thymus gland in amphibians, Dustin ('11, on Axolotl, and 

 '13, on Rana fusca) and Maximow ('12, on Siredon pisciformis and 

 Rana temporaria), only the latter gives a brief description of its 

 morphogenesis. He finds the five early epithelial bodies in Sire- 

 don in essentially the same position as described by Maurer ('02) , 

 and, although he observes darkly staining cell groups (what he 

 calls the 'thymus ectodermalis ' von Driiner) closely associated 

 with the thymus bodies on the one hand and with the correspond- 

 ing ganglia on the other (in the early stages — 7.5 to 15 mm. 

 larvae), he is not certain of the origin of these, and he says (p. 

 573), ''Ob diese Zellensammlungen wirklich dem Ektoderm en- 

 stammen, wie es Driiner will, vernag ich nich anzugeben . . ." 

 The true epithelial character of the bodies is retained but for a 

 short time (from the 7.5 to the 9 mm. stages), there soon appear- 

 ing other elements (p. 576), which increase in numbers in the 11 

 mm. and subsequent larval stages. He also substantiates the 

 results of the earher workers (especially Maurer '88, and Driiner 

 '04) concerning the early degeneration of the first two epithelial 

 bodies, and the persistance of the last three to form the definitive 

 gland, although he carries his work only through the 25 mm. 

 stage, appending the remark (p. 603) , ' 'spateren Entwicklungs- 

 stadien der Thymus beim Axolotl boten fiir mich kein Interesse 

 mehr . . . ." 



Postbranchial (suprapericardial or ultimohranchial) body 



This structure, which has been given different names by differ- 

 ent authors, was probably first described in the anurans (Rana 

 and Bufo), by Leydig ('53) as parts of the true thyreoid. (Greil, 

 ('05), says that Leydig described them as 'Glandes thyreoides 

 accessories,' but in Leydig's paper, I can not find that he men- 

 tions this name, and it is probable that Greil took this information 

 from de Meuron who uses this term, see p. 542.) Van Bemmelen 

 ('86) w^as the next worker who described the structure (in selach- 

 ians) and from its position in that group gave to it the name 

 'suprapericardial body.' Later, de Meuron ('86), p. 541, gave a 

 brief account of its development in Bufo. According to him, it is 



