102 PROCEKDIXGS OF THE ACADEMY OF [Feb., 



by shriukage at fixation. They are very deep and narrow and 

 seem filled completely by their cilia. 



The connective tissue covering (e.t.) of the thyroid, spoken of 

 in connection with the outward appearance of the thyroid, is seen, 

 in section, to form a thick layer entirely around the gland and to 

 form the central mass of median lamella (m.L). It also forms a 

 thick coating around each branch of the large artery which Dohrn 

 calls the Pseudobrauchial artery (Spritzlocharterie) (art.). The 

 large and now nearly enclosed space (i.v. ), formed by what was 

 called the " lateral invagination," is more or less completely filled 

 by a sort of reticulated tissue with scattered nuclei. This reticu- 

 lated tissue also fills the space between the floor of the pharynx and 

 the thyroid. Numerous small blood vessels are found imbedded in 

 it, both in that which fills the lateral invagination and in that which 

 lies between the gland and the pharynx. This tissue is represented 

 only in figs. 6a and 66, but the fibrous tissue is shown in all the 

 figures of this stage. 



Fig. 06 represents a section cut a short distance anterior to the 

 duct, at the point 6., fig. 6^, and about coi'responds to fig. 5^ of 

 the preceding stage. The ciliated grooves at this point have imited 

 to form a single deep groove, which is spread out at the bottom to 

 form the side pockets ( p. ) described in the preceding stage. The 

 lateral and median pairs of cell-groups have approached each other 

 until their adjacent groups are nearly or quite in contact ; at the 

 same time the ciliated layer (/./.) has increased somewhat in 

 length, and at its dorso -median angle (at the end of the lines/./., 

 fig. 66) its cells have changed from the tall columnar with small, 

 round nuclei to short cells, almost completely filled ^nth their large 

 oval nuclei and resembling the cells that lie close to the openings 

 (o. ) of the groups of the gland cells. It is this group of cells, 

 lying in the dorso-mediau portion of the ciliated layer, that sep- 

 arates into two about equal parts, a little further posteriorly, to 

 connect the gland with the deep ciliated groove, in the manner 

 described in the preceding stage and shown in figs. 5h-i of that 

 stage and in fig. 6c of tlie stage now under discussion. The ciliated 

 layer is somewhat folded, as though it had increased in length very 

 rapidly, or had been compressed by tlie shrinkage of the connective 

 tissue (c.t. ) surrounding the gland. There is considerable space at 

 this point between the i)havynx and the thyroid, which necessitates 



