K. T. Bell 53 
Fig. 8 (right side of figure), the central area has formed two large vacu- 
oles (v). On the left side of the same figure, a concentric vacuole (v) 
has formed, separating off a central spherical nucleated mass of proto- 
plasm. The nucleus of this mass of protoplasm is shrunken and the 
cytoplasm shows many small vacuoles. The corpuscle shown in Plate IT, 
Fig. 9, is probably a later stage of the form just described. The central 
protoplasmic mass has become converted into an ellipsoidal pale body 
(pm). The small circular body in this shriveled mass is probably the 
nucleus. Some corpuscles like the one shown in Fig. 9 are found in 
which the central mass has entirely disappeared. The further growth 
of corpuscles of this type seems to be by formation of colloid lamelle as 
in the ordinary type. They soon become indistinguishable from other 
forms. 
The cystic type of corpuscle is rare in the pig. This evidently cor- 
responds to the form in amphibia that misled Nusbaum and Machowski 
into reviving Afanassiew’s theory. The central masses, in Figs. 8 and 9, 
might readily be mistaken for red corpuscles in animals in which these 
cells are nucleated. But the red cells of the blood of the pig are not 
nucleated at this stage. I have traced a number of these corpuscles (as 
well as those of other types) in serial sections and have never seen any 
indications of a connection to blood-vessels. Nusbaum and Machow- 
ski (19), (Fig. 1, e, S. 116) show a corpuscle which is similar to my 
Fig. 9. It will be noted that the central space in neither of these figures 
is lined by endothelium. The early form of corpuscle shown by Nus- 
baum and Machowski (Fig. 1, d, S. 116) is very probably a normal blood- 
vessel with cubical endothelium. I have often found such vessels with 
cubical endothelium in the interlobular tissue of the pig’s thymus at 10 
em. to 12 em. They probably may be found at other stages also. In the 
thymus of a kitten, injected by the intra-vitam Prussian blue method pre- 
viously described, the majority of the corpuscles were found to be in 
early stages. The injection did not penetrate any corpuscle. I had a 
somewhat better opportunity to study the relations of the corpuscles to 
the blood-vessels in a 14 em. human embryo. Here the vessels of the 
thymus were all very much distended with blood and the corpuscles were 
in early stages. No blood cells were found in the corpuscles. 
(b) Compound concentric corpuscles are formed whenever two or more 
simple concentric corpuscles begin to form so close together that they 
come in contact during their later growth. An early stage of such a 
corpuscle is shown in Plate II, Fig. 15. The colloid lamelle are formed 
around each center until they come in contact; they are then formed 
around both centers. In Plate III, Fig. 22, a compound concentric cor- 
