557 



Nachdruck verboten. 



The Derelopmeut of the Thyroid Gland and of the Supraperi- 

 cardial Bodies in Necturiis. 



By Julia B, Platt. 

 With 9 Figures. 



In a paper entitled "Schilddrüse, Thymus and Kiemenreste der 

 Amphibien", Maurer^) describes the development of the thyroid 

 gland and suprapericardial bodies (postbranchial bodies) in Triton 

 taeniatus and Siredon pisciformis. Finding the process of 

 growth in these two forms essentially the same, Maurer concludes 

 that they furnish a type for the development of the organs in question 

 in the Urodela. 



He finds that the thyroid arises as a solid, unpaired, median, 

 outgrowth form the endodermic floor of the branchial cavity. This 

 outgrowth extends from the second branchial pocket to the an- 

 terior wall of the heart-cavity, and soon separates from its ground 

 of origin as an egg-shaped mass of cells, which ultimately di- 

 vides into two parts that come to lie on the lateral surface of the 

 sterno-hyoideal muscle, just posterior to the second ceratobranchial. 

 In consequence of the rapid change in position, after the partition of 

 the thyroid, there often remain in the median line between the 

 genio-hyoideal muscles, pieces of the isthmus which originally united 

 the two parts of the gland. These may develop into a small ac- 

 cessory thyroid. 



In addition to the thyroid , Maurer describes in the A n u r a 

 paired organs, which with de Meuron^), he homologizes with the 

 suprapericardial bodies found by van Bemmelen ^) in the Selachii. 

 Maurer prefers, however, to call the organs in question "postbranchial 

 bodies", as they always arise behind the last gill cleft, 

 and since to him their genetic relation to the branchial cavity seems 



1) Fe. Maureb, Morphologisches Jahrbuch, Bd. XIII, 1888. 



2) PiEEEE DE Meüeon, Recherches sur le developpement du thymus 

 et de la glande thyroide. Recueil zool. Suisse, T. III, 1886. 



3) J. F. VAN Bemmelen, Ueber vermutliche rudimentäre Kiemen- 

 spalten bei Elasmobranchiern. Mitteil, aus der Zool. Station zu Neapel, 

 Bd. VI, 1885. 



