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'\ 45:hey are deep and so narrow that there would seem to be but 

 little room for ciliary action. The cells lining the grooves 

 are here somewhat shorter than the other cells of the pharynx, 

 v/hereas more anterior sections showed the reverse to be the 

 case, as was mentioned above (Figs. 5 b-d) . 



The single ciliated chamber (considering one side only 

 of the bilaterally symmetrical gland) forms about three fourths 

 of a circle (m.c.h.) and is boimded by the cover cells (d.l.) 

 on the one hand and by the ciliate d cells (f.l.) on the other. 

 The cove r cells have become so much flattened that they from a 

 mere membrane, and their nuclei are pressed far apart. The 

 ciliated cells are of a typical ciliated columnar form, and are 

 exposed, at their ciliated ends, to the cavity that has been de- 

 scribed cs the ciliated chamber , and at their basal ends to the 

 space that is now a part of the lateral invagination (i.v.). 

 Several large blood vessels are seen, surrounded by the angular 

 mesoblast cells, and on each side of the thyroid, lying close 

 to the body wall, is a large longitudinal muscle. Before reach- 

 ing the point at which it opens into the thyroid, the groove 

 spreads out at the bottom (Fig. 5 g, p.) and resembles, in cross 

 section, an inverted letter T. The cross arms of the T turn 

 upward as they pass farther baokv/ards (Fig. 5 h, p.) until they 

 are closely pressed against the vertical part of the T. The v/ay 

 in which this curious groove opens, finally, into the thyroid 

 is interesting. A short distance back of the point represented 



