. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. No. 3.] OESOPHAGEAL GLANDS OF URODELA. 93 in chromatin. As the gland narrows into the duct (Fig. 3, b), these are replaced by two or three slightly larger cells, in each of which two zones may be recognized, an outer, wider, deeply staining zone containing the oval nucleus, and an inner one which stains but feebly. This inner zone exhibits a reticular structure due to the presence of a secreted substance, probably mucigen. In the more posterior tubular glands, likewise, two kinds of cells may be found, similar in all respect
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. No. 3.] OESOPHAGEAL GLANDS OF URODELA. 93 in chromatin. As the gland narrows into the duct (Fig. 3, b), these are replaced by two or three slightly larger cells, in each of which two zones may be recognized, an outer, wider, deeply staining zone containing the oval nucleus, and an inner one which stains but feebly. This inner zone exhibits a reticular structure due to the presence of a secreted substance, probably mucigen. In the more posterior tubular glands, likewise, two kinds of cells may be found, similar in all respects to those of the flask-shaped glands, granular cells occupying the body of the gland, mucigenous cells the neck. In sections stained in Reinke's neutral gentian it is found that already numerous zymogen granules are present in the deeply staining cells forming the body of the gland. In the pancreas, also, zymogen granules may be recognized long before the yolk granules have entirely disappeared from the cells. The epithelium of the foregut in the region occupied by the flask-shaped glands is com- ^ ^ a posed of two kinds of cells (Fig. 3, c), ciliated cells and cells the outer ends of which stain diffusely and intensely. These obviously FlG. ^blystoma represent the two characteristic elements of larvai2mm-inlength; , c ..... .... oesophageal gland. the future oesophageal epithelium, the cm- Apoch. 2 mm.,comP. ated and the goblet cells. Over the tubular ocular2- glands farther back there is only one kind of cell in the epithelium, and this is without cilia. Mitoses may be observed with equal frequency in all the various kinds of cell composing the epithelium and glands, and all are apparently equally capable of reproduction. The important points to be learned from this stage are that the characteristic elements of the glands are differen- tiated very early, that no special groups of cells have, as yet, assumed the mitotic function to the exclusion of the others, and. that a
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