MORPHOGENESIS OF THE FOLLICLES 413 



Remak ('55) described in chick embryos in the wall of the 

 jirimitive saccular, epithelial thyroid anlage the formation of 

 thickenings which become separated and later give rise to the 

 thyroid follicles. He also thought that the original saccular 

 anlage might persist for some time and form new secondary 

 vesicles by a process of constriction. He described similarly the 

 origin of secondary follicles, both by constrictions and by solid 

 budding, in the thyroid of pig fetuses four inches and above in 

 length. 



Peremeschko ('67) described the division of primary into sec- 

 ondary follicles in mammahan fetuses. Colloid is described as 

 arising partly by secretion and partly by colloid metamorphosis 

 of epithelial cells. 



W. Miiller ('71) described a developmental stage in which 

 the thyroid consists of a network of cylindrical tubes. Such 

 tubes were found in a 24 mm. fetus and in decreasing numbers 

 in later fetuses and even in a three year old child. These tubes 

 arise from solid epithelial cords by the development of a central 

 lumen. The segmentation of the tubes with the formation of 

 the gland-vesicles is produced by ingrowth from the mesoblast. 



Horcicka ('80) found the thyroid gland of a four months' fetus 

 to be made up for the most part of solid cell masses with a be- 

 ginning of lumen formation in the central cells of these masses. 

 Typical gland structure is found after the fifth fetal month. 



Wolfier ('80) described the formation of follicles from sohd 

 masses of epithelial cells. Toward the end of the fetal period 

 and after birth the peripheral cells of the groups dispose them- 

 selves in a circle. The central cells become at first granular, 

 then degenerate and disappear in the pale, granular mass 

 which fills the lumen of the vesicle thus formed. 



L. Stieda ('81) noted that the anastomosing epithelial cords 

 ('Epithelstrange') of the embryonic, mammahan thyroid are at 

 first always solid, but that in the ends of these cords lumina 

 appear, and the resultant vesicles are gradually constricted off. 



Baber ('81) described the fully formed follicle as spheroidal 

 in form, but observed also branching follicles which are prob- 

 ably giving rise to secondary follicles by a process of division. 



