the pharynx as was the case in previous sections, being separated 

 from the wall, of the pharynx by a collection of mesoblast cells. 

 The cavity of each half of the gland is crescentic in cross 

 section, and on the left side Is seen the beginning, of the lat- 

 eral invagination. 



The thyroid cavity is closed in now for about 2/5 of 

 its entire length, both anteriorly and posteriorly, so that its 

 opening into the pharynx is reduced to a slit extending only 

 1/5 the length of tile gland. 



Sections through the thyroid, anterior to this opening 

 (Fig, 2 b, ) but posterior to the divided portion of the anterior 

 end, show the cavity to be considerably complicated by the thick- 

 ening and folding of the walls. The simple, circular cavity 

 of the preceding stage (Fig. lb,) is now reduced, by the growth 

 and invagination of the walls, to a narrow vertical slit with 

 lateral diverticula above and below, giving the cavity, in cross 

 section, somewhat the shape of a distorted letter ?, The dorsal 

 wall of this cavity (Pig. 2 b,, d.l,) is comparatively thin, being 

 composed of a single layer of rather short col'umnar cells, and 

 is what Dohrn calls the "Decklamelle, " The ventral wall is also 

 comparatively thin, and shows in the centre, at the extreme 

 anterior end of the unpaired cavity, a slight upward projection 

 (Fig, 2 b, ra.l,) which would seem to be the first indication 

 of the medial longitudinal partition that will later divide 

 the gland into two lateral parts. According to Dohrn, this me- 



