MORPHOGENESIS OF THE FOLLICLES 417 



Broinaii ('11) described in the differentiation of the thyroid 

 anlage a tubular stage transformed by constrictions into beaded 

 chains and finally into separate folhcles. 



According to Grosser ('12), the thyroid anlage begins to sepa- 

 rate into solid cords in the human embryo of 8 mm. In the 50 

 mm. fetus the cords, especially in the periphery, appear beaded. 

 The beaded cords become divided into separate cell-masses, the 

 anlages of the follicles. The lumina may appear as independent 

 cavities (no tubular stage), before the follicles are detached, or 

 they may arise later even in early postnatal life. 



Simpson ('12) referred to the tubular structure of the thyroid 

 and describes the gland of a seven months old child as tubular 

 in character. 



Aschoff ('13) stated that in the developing thyi'oid gland con- 

 nective tissue separates round epithelial balls from the anasto- 

 mosing cords, and it is in these 'balls' that the folUcular lumina 

 develop. 



Sobotta ('15) described the first lumina as appearing in the 

 peripheral parts of the lateral thyroid lobes in a fetus 50 mm. in 

 length. The final breaking up of the cell cords into single 

 groups, which will later form folhcles, progresses very gradually, 

 so that the final structure of the gland is arrived at only after 

 birth. InterfolUcular epithelium persists, which may later give 

 rise to follicles. 



Kingsbury ('15) in describing the early development of the 

 thyroid states that lumina (folhcular cavities) appear within the 

 cell cords in fetuses of 32 mm., but colloid is not demonstrable 

 until 40 mm. 



III. MATERIAL AND METHODS 



This study is based upon the collection of human embryos in 

 the Anatomical Laboratory of the University of Minnesota. 

 Several of the series used are in excellent condition for histo- 

 logical study. The embryos of the collection have been vari- 

 ously fixed and stained. The additional glands specially pre- 

 pared have, for the most part, been fixed in Formol-Zenker; 

 embedded in paraffin, sectioned at 10 m; mounted serially and 



