PHARYNGEAL DERIVATIVES OF AMBLYSTOMA 653 



addition, that the gland- had since been studied in Nee turns 

 (probably referring to Miss Piatt's work), but other than this 

 makes no further comment. Muthmann ('04), repeating some 

 of the earlier work by Brachet ('98), followed the very early 

 development of the thyreoid anlage in a number of urodeles^ 

 (Triton alpestris, Axolotl, Salamandra atra) and also certain 

 anurans (Bufo vulgaris and Rana temporaria) with special refer- 

 ence to its position relative to the heart anlage. In Triton 

 alpestris the anlage of the gland is laid down very early in the 

 embryo (as early as the endothelium of the heart), and in a 20 to 

 21 somite specimen, it was a solid bud of cells on the floor of the 

 pharynx, just in front of the bulbus arteriosus; later (25 somites), 

 this elongated slightly and lay between the right and left man- 

 dibular arteries. In the 30 somite stage the caudal end had 

 elongated a little, but the proximal end was still connected with 

 the pharynx, and remained so for the first four days of larval life. 

 Muthmann made no serious attempt to follow its development 

 beyond this stage, remarking, (p. 43), ''Genauere Beschreibung 

 dieser Vorgange geben Maurer und Livini." 



Driiner ('04) notes the position of the thyreoid with reference 

 to certain adult structures in Siredon pisciformis, but contributes 

 nothing to our knowledge of its development. Marcus ('08), has 

 described the development of the thyreoid gland in Hypo- 

 geophis, where he found, instead of the solid early anlage (as in 

 urodeles and some anurans), a hollow one, similar to that de- 

 scribed by W. Miiller ('71), for Rana, and Goette ('75)- for 

 Bombinator. 



Finally, Mrs. Thompson ('10), in a paper on the thyreoid and 

 parathyreoids throughout the vertebrates, gives a very brief study 

 of this gland in the amphibians. She bases her study on a single 

 species of urodele (Spelerpes ruber, adult) and on the frog (men- 

 tions no genus nor species), and since she gives no details of its 

 development, only passing mention need be made here. She 

 shows however, a drawing (pi 10, fig. 4) of the histological struc- 

 ture of the adult gland in Spelerpes, which she claims is the first to 

 be given for any urodele. 



Thymus. The position of the thymus in the adult amphibians, 



JOURNAL OF MORPHOLOGY. VOL. 30, NO. 2 



