MORPHOGENESIS OF THE FOLLICLES 415 



Hiirthle ('94) described in the thyroid of young dogs scattered 

 masses of interfolUcular epithelium, in which new (primary) 

 foHicIes arise by the secretion of colloid into the angles between 

 adjacent cells. 



Anderson ('94) described secondary folUcles (postnatal) aris- 

 ing from the collapsed epithelium of emptied follicles in various 

 mammals. The new lumina are formed by cell-secretion of 

 chromophile spherules. 



According to L. R. Mliller ('96), the origin of small secondary 

 follicles from the larger follicles, as described by Ribbert ('89) 

 is clearly evident, even in the human adult. 



Tourneux and Verdun ('97) in a careful study of the branchial 

 derivatives in the human embryo described the transformation 

 of the (median) thyroid plate (and later of the lateral thyroid 

 anlage) into a richly anastomosing network of solid epithelial 

 cords by ingrowth of vascular connective tissue in a 14 mm. 

 embryo. This network was likewise observed in embryos of 

 19 mm. to 37 mm. in length. At 37 mm., the cords become 

 varicose, and follicles develop by the formation of a cavity 

 within each of the enlargements. A similar process of morpho- 

 genesis is described in the rabbit embryo by SouUe and Verdun 

 ('97). _ 



Streiff ('97) made wax reconstructions of normal, adult 

 human thyroid tissue, and found it to be made up of closed fol- 

 licles, ovoidal or spindle shaped. Branched forms due to 

 budding or to secondary fusion were also described ; some of these 

 more complex forms he thought may represent persistent branch- 

 ing, a continuation of the embryonic process. He concluded 

 that the thyroid arises as a branched tubular gland, the follicles 

 being formed by constriction of the tubes. 



Schreiber ('98), in a fetus of three months, found the thyroid 

 gland for the most part arranged into follicles which contained 

 much colloid. 



Kiirsteiner ('99) in fetuses from 8 to 30 cm. in length found 

 the thyroid lobules made up of round or elongated, solid or 

 hollow folhcles. The lumina are few in number up to about 20 

 cm., but in the older fetuses they are numerous and evenly 



