60 The Development of the Thymus 
24. Scuarrer, J.—Ueber den feiieren Bau der Thymus und deren Beziehung 
zur Blutbildung. Sitzungsber. d. K. Acad. d. Wissensch. Math.- 
naturw. Kl. Wien., Bd. CII, Abt. III, 1893. 
25. Scuepet, J.—Zellvermehrung in der Thymusdrtise. Archiv f. mikr. 
Anat., Bd. XXIV. 
26. Sriepa, L.—Untersuchungen tiber die Entwickelung der Glandula Thy- 
mus, Glandula Thyroidea, und Glandula Carotica. Leipzig, 1881 
(cited from Hermann et Tourneux). 
27. Sutran.—Beitrag zur Involution der Thymusdriise. Virchow’s Archiv, 
Bd. 144, 1896. 
28. Ver Eecke.—Structure et modifications fonctionelles du thymus de la 
grenouille. Bulletin de l’Académie royale de Médicine de Belgique, 
1899. 
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ay, ssl. Sh Aa 
30. Watiiscu.—Zur Bedeutung der Hassall’schen Korperchen. Archiv f. 
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nant). 
EXPLANATION OF PLATES. 
All the figures were drawn with Leitz obj. 1/12, oc. 4, and camera lucida. 
The magnification after the reduction of the plates is about 1060 diameters. 
All drawings were made from transverse sections of the mid-cervical seg- 
ment of the thymus unless they are otherwise indicated. 
The following abbreviations designate the structures indicated in all the 
figures: 
c f—colloid in formation. 1p n—large pale nucleus. 
cl—caleareous deposit. m—nucleus in mitosis. 
ce s—solid colloid. md—beginning of medulla. 
ces d—solid colloid that stains n—nucleus. 
deeply. o c—old colloid. 
e—erythrocyte. p m—protoplasmic mass. 
end—endothelial nucleus. sf—fibril in syncytium. 
I—lymphocyte. ss—space in syncytium. 
lb—lymphoblast. v—vacuole. 
1d n—large dark nucleus. 
PLATE I. 
Fic. 1. From a 3.7-cm. pig embryo. Stained with iron-hematoxylin and 
Congo red. Vacuolization of the cytoplasm and differentiation of the nuclei 
have begun. 
Fic. 2. From the thoracic segment of a 4.5-cm. pig embryo. Stained with 
iron-hematoxylin and Congo red. A cellular reticulum is now formed. Large 
pale nuclei, lymphoblasts, and the large dark intermediate forms are present. 
Fig. 3. Epithelioid type of concentric corpuscle. From a 16-cm. pig em- 
bryo. Stained with hematoxylin and Congo red. Colloid lamelle (c s d) 
