92 J. A. BADERTSCHER 



median thyroid anlage, however, is derived the larger part of 

 the structural elements of the thyroid gland. 



According to Christiani, in rodents (rat) the lateral thyroid 

 gives rise to an epithehal body.^ 



Maurer ('99) finds that in the Echidna the postbranchial 

 bodies do not fuse with the median thyroid anlage. In the 

 adult condition the thyroid lies posterior to the postbranchial 

 bodies. The latter are represented by two alveolar structures 

 which developed colloid (judged by staining reaction). The first 

 traces of colloid formed in the postbranchial bodies appears, 

 however, in later developmental stages than does that of the 

 median thyroid. 



Prenant ('94) finds that in sheep embryos the lateral thyroid 

 develops into a central canal with an irregular lumen from the 

 walls of which cell cords and cell masses (recognized by their 

 dense structure) extend into the substance of the median thyroid. 

 An intimate fusion takes place between the lateral and medial 

 elements. In later developmental stages the tissue, which in 

 earlier stages can be recognized as derived from the lateral thy- 

 roids, disappears. He was unable to determine whether or not 

 the lateral thyroids contribute to the structural elements of the 

 gland. 



In this brief historical sketch the following views as to the 

 fate of the ultimobranchian bodies were brought out : (1) They 

 contribute to the structural elements of the thyroid gland; (2) 

 They develop into cysts; (3) They develop into a gland of a dif- 

 ferent structure from that of the thyroid gland; (4) They develop 

 into epithehal bodies, and (5) They disappear entirely. 



III. MATERIAL AND METHODS 



The material used for this investigation was collected in great 

 abundance at a packing house. The upper jaw, cranium, and 

 thorax were removed from embryos ranging from 15 to 25 mm. 

 in length. The part containing the thyroid was thus made com- 

 paratively small and fixed well. From embryos 26 to 75 mm. in 



» Cited from Zuckerlandl ('03). 



