62 The Development of the Thymus 
by the deeply-staining colloid. The neighboring nuclei are beginning to 
show the effect of the centrifugal pressure. 
Fic. 14. Ordinary concentric corpuscle in an early stage. From a 10.5-cm. 
pig. Stained with hematoxylin and Congo red. A band of deeply-staining 
colloid has been formed. Just outside this is colloid in formation. 
Fie. 15. Two simple concentric corpuscles which would have formed a 
compound concentric corpuscle. From a 10.5-cm. pig. Stained with hema- 
toxylin and Congo red. The left corpuscle is a little more advanced than 
Fig. 11. The right corpuscle shows a large area of deeply-staining colloid 
which has pressed the nucleus into a small irregular shape. 
PrATH TT: 
Fig. 16. Compact irregular corpuscle in an early stage. From a 14-cm. 
pig embryo. Stained with hematoxylin and Congo red. The colloid is not 
yet solid. The nuclei are not essentially different from those of the adjacent 
syncytium. 
Fic. 17. Ordinary concentric corpuscle. From a 12-cm. pig embryo. 
Stained with hematoxylin and Congo red. There is a large, central, deeply- 
staining colloid mass in which calcareous deposits (cl) have been made. 
The neighboring nuclei show the effects of the centrifugal pressure. 
Fic. 18. Epithelioid concentric corpuscle in an early stage. From a 10.5- 
cm. pig embryo. Stained with hematoxylin and Congo red. The outer col- 
loid lamella marks off a nucleated mass of cytoplasm resembling a large cell. 
The nucleus is undergoing the same changes as occur in the central nucleus 
of an ordinary concentric corpuscle. 
Fic. 19. Compound concentric corpuscle. From a 10.5-cm. pig embryo. 
Stained with hematoxylin and Congo red. This would have soon lost all 
evidence of its compound nature. 
Fic. 20. Epithelioid concentric corpuscle. From a 10.5-cem. pig embryo. 
Stained with hematoxylin and Congo red. Some colloid is forming outside 
the circular area. Solid deeply-staining colloid is forming. 
Fic. 21. Ordinary concentric corpuscle, showing a variation from the 
usual type. From a 16.5-cm. pig embryo. Stained with iron-hematoxylin 
and Congo red. The central nucleus is reddish but not enlarged. No solid 
colloid has been formed. 
Fic. 22. Compound concentric corpuscle. From a 16.5-em. pig embryo. 
Three centers are present. The pale colloid in the upper part is probably 
older than the deeply-staining variety. In the lower part of the figure, a 
young corpuscle is shown. 
Fic. 28. Compact irregular corpuscle. From a 16-cm. pig embryo. Stained 
with hematoxylin and Congo red. Some of the colloid is solid. No definite 
center is present but one is beginning to form (c s). The nuclei are not 
markedly different from those of the adjacent syncytium. 
