PHARYNGEAL DERIVATIVES OF AMBLYSTOMA 647 



pharyngeal tube, its appearance in the larva at the time of meta- 

 morphosis, and its close relationships to the epithelial bodies in 

 their development, leads to its consideration here. 



Different views are held regarding the origin of this gland in the 

 anurans and the urodeles. Maurer ('88), described its develop- 

 ment in anurans from the first branchial pouch, and was inclined 

 to believe it had a similar origin in the urodeles. Zimmermann 

 ('98) considered it simply as an enlargement of the walls of the 

 blood vessel in anurans, and Boas ('83) earlier suggested this was 

 the case in Salamandra. Maurer ('02, p. 152) says: 



Dies Organ ist hier anziischliessen. Nacli der Auffassung vieler 

 Authoren ist sie eine blosse Gefassbildung, durch Wucherung der 

 Gefasswandung enstanden. Da Andere aber eine Beteiligung von 

 Schlundspaltenepithel angaben, so ist sie hier zu erwahnen. Bei 

 Anuren fand ich im Bereich der 2. Schlutidsplate eine epitheliale 

 Knospe, die sich genau so verhalt wie die Epithelkorperchen der 3. und 4. 

 Spalte, aber eben durch ihre sehr bald erkennbare Beziehung zur Kie- 

 menarterie sich eigenartig erweist. Nach Zimmermann ist eine Epi- 

 thelknospe nicht vorhanden, und nur eine Wucherung der Gefasswand 

 bildet die Driise. 



In Amblystoma the carotid gland and the two epithelial bodies 

 begin their development during metamorphosis. The carotid gland 

 is the first to appear, its anlage forming on either side, in the region 

 where the first afferent branchial artery enters the gill. The 

 anlagen of the two epithelial bodies of either side appear at first 

 some distance caudad and medial to one another and to the ca- 

 rotid gland; but as development proceeds they are brought closer 

 and closer together so that in late transforming and adult stages, 

 one lies posterior to the other. 



A. Transforming Amblystoma larvae. In the early transform- 

 ing stage, the caudal pharyngeal pouches are being reduced, the 

 fourth and fifth slits being completely closed to the exterior. 

 The carotid gland is just beginning as a slight enlargement of the 

 wall of the first afferent branchial artery in the region where it 

 enters the first gill-arch, this enlarged portion being augmented 

 by the union of the external carotid artery in front, and the inter- 

 nal carotid artery close behind. At the same time there is a 

 noticeable thickening of the walls of the enlarged portion (anlage 



