CARCINOMA OF THE THYROID IN SALMONOID FISHES. 489 



118.) Passing toward the center of the lobe there are marked degenerative processes 

 in the tissue. The clefts become fewer in number, the epithelium stains less irregu- 

 larly than before, the irregular alveolar openings are fewer, and the whole tissue is com- 

 posed of a confusion of cells with just a suggestion of the previous clefts representing 

 the old alveoli (fig. 117), which in this region appear to be filled by desquamated and 

 rather poorly staining cells. 



At the very center of the lobe the evidences of degeneration are more intense. 

 One finds masses of cell complexes, deeply staining and homogeneous protoplasm. 

 The cell boundaries are destroyed, the nuclei, although still staining deeply, are embedded 

 in the protoplasmic structure with only the most ill-defined suggestion of cell bounda- 

 ries to the protoplasm. (Fig. 119.) At the peripheral portion of the lobe where the 

 papillary adenomatous type of tissue is well preserved, no evidences of degenera- 

 tion are to be found. One finds in various places in the capsule evident invasion of 

 this structure. The capsule is thick, composed of fibrous connective tissue with small, 

 deeply stained connective tissue nuclei. In the dense fibrous structures of this capsule 

 at various points definite alveoli lined with high columnar epithelium are found, extend- 

 ing in some instances to the outermost limit of the thick capsule. Under high power 

 the epithelium of these alveoli and the capsule is found to be high columnar, most of 

 the nuclei staining deeply and homogeneously, but here and there are vesicular nuclei 

 with one or more nucleoli. The epithelium is in some of these alveoli several layers 

 thick; the protoplasm stains deeply with a cytoplasmic stain. Some of the larger nests 

 of cells in the capsule have almost lost their alveolar stnicture and formed more or less 

 compact islands of cells, with nuclei varying in size, many of them vesicular. 



In the margins of such a complex of cells one finds direct invasion of the dense 

 connective tissue structure of the capsule, there being no stroma between the vesicles 

 and no delimiting membrane to them. In fact, indi^^dual cells can be found invading 

 the connective tissue fibers. Occasional karyokinetic figures are found and about the 

 larger masses of cells described there are evidences of expansive growth in the arrange- 

 ment of the immediate encircling fibers of the capsular structure. 



Under high power the outer zone of adenomatous proliferation shows great varia- 

 bility in the nuclei of the cells, most of them being vesicular, with one or two nucleoli. 

 They vary in form from elongate to oval and spherical, mostly oval. The smaller nuclei 

 stain more homogeneously than the larger ones, the epithelium covering the papillary 

 projections is high columnar, the protoplasm stains diffusely, and occasional cells are 

 found in this region in which a swollen and cloudy appearance of the protoplasm indi- 

 cates the first evidence of degeneration. The stroma of the papillae is not well devel- 

 oped. The capillaries are plentiful but do not form a prominent part of the picture. 



Approaching the center of the lobe, large irregular clefts, made up by the papillary 

 projections, are less in evidence and large areas are found in which the epithelium pre- 

 sents peculiar forms and a swollen, cloudy appearance of the protoplasm. The cells are 

 of the most bizarre form and shape, often are spindle shaped, and what has previously 

 been the alveolar spaces in the cells are filled with closely packed, desquamated epi- 

 thelium. The nuclei here still stain well, are vesicular in character, and vary greatly 

 8307°— 14 9 



