BT Bell ol 
well-known onion-like structure found in the fully-formed corpuscle. 
The nuclei that are enclosed between the lamelle gradually lose their 
chromatin and become flattened out. They do not swell and are not 
obliterated. It seems that swelling occurs only in nuclei that are sur- 
rounded by deeply staining colloid, and that this change is preparatory to 
their obliteration by or transformation into colloid. The amount of the 
corpuscle that breaks up to form the softer center is very variable. 'The 
size of the center usually seems to increase with the age of the corpuscle. 
Plate III, Fig. 21, shows a variation from the ordinary concentric 
type. ‘The central nucleus (7) stains reddish but is not enlarged. Most 
of the other nuclei are unchanged. All the colloid (c¢ f) is in the early 
fibrous and granular stage. 
From 20 cm. to full term many corpuscles show masses of calcareous 
material in or near the center. This material rarely appears in younger 
corpuscles (Plate III, Fig. 17, ¢7). It stains a violet blue with Dela- 
field’s hematoxylin. 
The majority of the corpuscles of Hassall belong to the ordinary type 
of simple concentric corpuscles described above. It is very clear that 
they have nothing to do with blood-vessels. They never contain eryth- 
rocytes nor anything resembling them. Rarely a lymphoblast or leuco- 
cyte is found inside the corpuscle. These seem to be usually involved in 
the corpuscle lke ordinary stroma nuclei during the formation of the 
lamelle. (Their occurrence in other types will be discussed later.) It 
is also clear that these corpuscles arise from the syncytium of the 
medulla. They are epithelial in origin, since the entire stroma of 
the gland is derived from epithelium, but they are certainly not remnants 
of the original epithelial anlage. Neither are they formed from lymphoid- 
like elements that reassume their epithelial nature as Maurer described 
for the lizard. 
Some of Ammann’s observations are in accord with my results. The 
swelling of the nucleus was noted by Ammann as the first step toward the 
formation of the corpuscle. {t should be noted, however, that rarely a 
corpuscle begins to form as a mass of colloid out in the cytoplasm and 
involves nuclei secondarily. I cannot distinguish his “Stadium der 
Transparenz ” for I cannot be sure that a corpuscle is beginning to form 
until some colloid is present. The formation of the colloid is associated 
with the swelling of the nucleus. His other three stages, “ Stadium der 
“Stadium der Verkalkung,” and “Stadium des 
> 
colloiden Entartung,” 
Zerfalls ” are easily seen. I have never seen corpuscles begin in leucocytes 
as Ammann described. His statement that the corpuscle grows by ap- 
position of reticulum cells is true in a modified sense. He thought that 
