94 
BULLETIN OF THE BUREAU OF FISHERIES 
are to be distinguished from the nuclei of the cylindrical epithelial cells by the fact that 
they are smaller in size and more round in outline and stain more intensely. The 
diameter of these cells is from 3 to 4 /i, while the long diameter of the oval nuclei of 
cylindrical cells is 5 to 6 a, or even 10 /« in younger salmon. Occasionally through the 
epithelial coat scattered leucocytes are found in the outer third of the layer. In fact, 
these cells may be located at any level from the general nuclear region to the surface 
border of the coat. They do not appear to be, at least have not been observed, escap- 
ing from the epithelial coat into the intestinal cavity. 
No eosinophile granule cells of any kind have been found in the alimentary epi- 
thelial coat of the king salmon. Such cells are described in this region for Proteus by 
Oppel. This observation is of importance in association with the fact that granule cells 
of a type already described above compose the stratum granulosum. 
Tunica propria . — The tunica propria of the caeca extends from the epithelial layer 
to the stratum compactum. Its extent varies greatly, and its outlines are very irregular. 
On the epithelial surface the tunica must follow the irregularities of that coat, while 
next the stratum compactum it is equally sinuous, owing to the great irregularity of 
surface of the stratum. The whole outline is not unlike that in the intestine, though 
simpler. 
The tunica propria is a connective tissue structure carrying numerous blood vessels 
and supporting a number of special types of cells in its meshes. The connective tissue 
fibrils form an open meshwork of the usual areolar type. (See fig. 9, pi. xxviii.) At 
its epithelial boundary it forms a very definite limiting membrane, the basement mem- 
brane, on which the epithelial cell layer rests. From this basement membrane the 
more or less open meshwork of fibrils begins. Numerous oval nuclei appear in the 
ground substance. The compactness of the tissue and the relative number of nuclei 
vary extremely in the various specimens. Where the tunica propria extends up into 
a fold of epithelium its tissue usually appears somewhat more compact. Definite loops 
of small blood vessels and capillaries are present in these projections. Open tissue 
spaces are found both in the loops and in the broader expanses of the coat just within 
the stratum compactum, in the normal tissue these spaces being small in size. Beside 
the proper nuclei of the connective tissue there are relatively large numbers of nuclei 
of the white corpuscle type belonging to cells that have not yet been comparatively 
studied. These cells vary extremely in number in different areas and in different 
salmon. 
The small arteries and veins, as well as the capillaries, are readily distinguished by 
the red corpuscles, which possess characteristic oval nuclei that take certain dyes in a 
differential way. Here and there are present certain large cells with a lightly stained 
cell body and a characteristic large nucleus, the identity of which has not yet been 
determined. 
Tying just within the stratum compactum are scattered granule cells. These 
granule cells usually lie next the stratum compactum, sometimes in its loops, but occa- 
sionally may be found near the deeper loops of basement membrane, never in the epi- 
thelial coat. In fasting salmon this group of granule cells is more prominent. 
