654 FRANCIS M. BALDWIN 



and something of its morphology in the various forms has long 

 been known. Simon ('44), observed it in Necturus Amphi- 

 uma and Cryptobranchus, and described its appearance and posi- 

 tion in these forms. Soon after, Ley dig ('53), in addition to the 

 forms studied by Simon, described the structure in Proteus, 

 Siredon, Caecilia annulata and a number of anurans. Its posi- 

 tion, according to Leydig, is, in both the anurans and the urodeles 

 close behind the angle of the jaw, superficially placed beneath the 

 skin. In the Caecilians, he noted four small bodies, one behind 

 the other just behind the angle of the jaw. The nerve supply of 

 the thjrmus was first noted by Fischer ('64), especially in Siredon 

 pisciformis, as the cutaneus ramus of the vagus. 



Goette ('75) was the first to study the development of the thy- 

 mus in amphibians. He described it in Bombinator igneus as de- 

 veloping from the dorsal portion of the second gill-pouch, but at 

 first he did not believe this to be the true thymus, preferring to 

 call it the ' Halsdriise. ' Later, de Meuron ('86) described the 

 development in Bufo and Rana, as an epithelial body arising from 

 the dorsal region of the second gill-pouch. This early separates 

 from the rest of the epithelial cells, and soon contains cells which, 

 in nature and appearance resemble those of the connective tissue. 

 This he called the tiue thymus, and homologized it with the first 

 thymus body of selachians. Maurer ('88), was the first to follow 

 the development of it in the urodeles (Siredon pisciformis, Sala- 

 mandra maculata and Triton' taeniatus). Briefly stated, he 

 found that in Siredon, five epithelial bodies were concerned in its 

 genesis, the first two of which early degenerated and the three 

 posterior ones remained. In Salamandra, three such epithelial 

 bodies developed, which he thought could be looked upon as the 

 homologues of the three persisting bodies in Siredon. In Triton, 

 the anterior two early degenerated, while a single large bean- 

 formed body remained some distance behind, which he was unable 

 to follow in its developmental stages. Whether this was formed by 

 the fusion of the three posterior bodies, as in the case of Siredon, 

 or whether it was formed solely from the last he could not say. 

 ''Jederfalls ensteht die Urodelenthymus aus dorsalen'Epithsl- 

 knospen hinterer Kiemenspalten, wiihrend- die zweite Knospe, 



