1086 
DR. H. WATNEY ON THE MINUTE ANATOMY OF THE THYMUS. 
the nucleus occasionally divides, as some of these cells contain several nuclei (see 
Plate 88, fig. 31, g). Sometimes, hut not often, the contained granular mass is 
nucleated (see Plate 89, figs. 44 D and E, and 45 A, gr). This form of granular 
cell might with equal reason be described as epithelioid connective-tissue-corpuscles 
containing granular masses; and presently, when we come to consider the origin of 
the granular cells, we must lay great stress on this variety. These cells are generally 
situated near to one or more concentric corpuscles or to giant cells (see Plate 90, fig. 49). 
Traces of a reticulum can be seen among them (see Plate 88, fig. 31, r). 
The second kind of granular cells are those which are vacuolated, and contain 
granular masses in their interior. They are generally polygonal or spheroidal (see 
Plate 88, fig, 32 ; and Plate 89, figs. 45 B, va, and 45 C, vci), and are found in most cases 
close to those of the first kind, and appear to arise from them, the clear protoplasm of 
the cell having shrunk away from the . granular mass. These vacuolated cells are 
found in some animals, as in the Bird (see Plate 95, fig. 98), in greater numbers and 
of much larger size than in Mammalia. This vacuolation of the cell, as we shall see 
afterwards, is a process of great importance in the formation of concentric corpuscles 
in some animals, and in the formation of the ciliated cysts in the Dog. 
If the vacuolation of the cell proceeds further the granular mass is set free, and can 
assume an independent existence. 
We then have the third form of granular cell, as met with in Plate 88, fig. 30, 
and Plate 89, figs. 46 D and E. In the two latter figures the granular mass is also 
vacuolated. In Plate 88, fig. 30, we find large granular masses, enclosed in a network 
of connective-tissue ; the granular masses may be considered as separate cells. In 
preparations of the thymus which have been shaken, we often meet with branched 
networks of connective-tissue-corpuscles, from which most of the granular cells have 
been shaken out (see Plate 93, fig. 78). 
The fourth variety of granular cells are club-shaped or rounded, and are attached 
to the blood vessels and the connective-tissue trabeculae (see Plate 85, fig. 8 ; Plate 
88, figs. 37, 38 ; and Plate 92, fig. 69). They are evidently not merely lying in 
apposition to these structures, but attached to them ; as shaking for a long time 
(three or four hours) does not separate this connexion. Those which are attached 
to the vessels sometimes appear to be entirely formed of a granular mass (see Plate 
92, fig. 68, and some of the cells in Plate 88, fig. 37), at other times of a clear 
protoplasm, nucleus, and granular mass (see Plate 88, fig. 35 ; and Plate 89, fig. 43) ; 
the latter stains of a different colour to the nucleus (see Plate 85, fig. 8). The lumen 
of the vessels appears to be quite unchanged (see Plate 85, fig. 8 ; and Plate 89, fig. 43), 
and there are no extravasations in the neighbourhood, nor any other feature to indicate 
that these cells have passed out from the vessel. The vessels have at times, however, 
a considerable thickening of the adventitia (see Plate 88, figs. 35 and 37). 
The granular cells attached to the connective-tissue trabeculae are well shown in 
Plate 88, figs. 36 and 37, and Plate 92, fig. 69, gr. In Plate 92, fig. 69, there are 
