-32- 



groups. As in the preceding stage^ the dorsal edge of this ridge 

 is at times somewhat thickened. 



The space between the anterior end of the coil and the 

 duct is short, as is seen by Pig. 6 k, and a section through the 

 gland in this region (Figt 6 d) differs very little from a cor- 

 responding section on the preceding stage (Fig. 5 j) except in 

 the particulars already pointed out for the anterior end of 

 the gland. The median ciliated chamber (m.o.h.) is long and 

 narrow in a dorso-ventral direction and its dorsal part is made 

 up of the shorter form of ciliated cells. The lateral ciliated 

 chamber (l.c.h.) is also much more extensive than in the preced- 

 ing stage. The ciliated groove (v. e.g.) is seen above the gland 

 in the floor of the pharynx. It is much less deep than it was 

 just anterior to the duot> and remains in about this condition 

 to a point beyond the extreme posterior end of the gland. 

 There is still a considerable space between the thyroid and the 

 floor of the pharynx, which space is filled with the reticulated 

 tissue mentioned above and shovm in '^igs. 6 a and 6 b. 



The following four sections (Figs. 6 e-h) all pass 

 through the coiled posterior end of the gland, at the points 

 indicated by the corresponding letters in Fig, 5 k. The appar- 

 ent complexity of these four sections will be made plain by com- 

 paring them v^ith the diagrammatic lateral viev; of the gland 

 (Fig. 6 k). In all four sections, what v;e have called the lat- 

 eral pairs of cell-groups (l.c.g.) remain the same and may be 



