PLATE 3 



KXPLANATION OF FIGURES 



5 Camera lucida drawing of a portion of a thymic lobule in a 36 nun. enibrjo 

 to show specially epithelial nuclei in various stages of degeneration. 1.5 mm. 

 Zeiss App. objective, X 8 Comp. ocular; reduced one-half. 



6 Camera lucida drawing of a portion ot a lobule of the thymus in a 55 mm. 

 embryo to show especially free nucleated and non-nucleated red blood-cells. 

 In the portion drawn one erythroblast is in mitotic division while several are in 

 amitotic division. 1.5 mm. Zeiss App. objective X 8 Comp. ocular; reduced 

 one-half. 



7 Diagrams showing the different types of cells that are derived from mesen- 

 chymal cells. The direction of the arrows shows the relation of the different types 

 of cells to each other; a, mesenchymal cell; b, c and d, transforming mesenchymal 

 cells; e, large lymphocyte;/, small Ijmtiphocyte; g and h, erythroblasts; i, normo- 

 blast; j, erythrocyte; k, lymphocyte capped with a layer of hemoglobin; I, m and 

 n show the formation of eosinophile leucocytes, and o and j), phagocytes; o, b, 

 k and p are camera lucida drawings while the remainder are free-hand drawings 

 from actual specimens. All were drawn from specimens in the interlobular 

 septa of a 125 mm. embryo excepting o and p, which were drawn from specimens 

 in an interlobular septum of a 110 mm. embryo. 1.5 mm. App. objective, X 8 

 Comp. ocular; reduced one-half. 



8 Camera lucida drawing of a portion of an interlobular septum of the thy- 

 mus in a 165 mm. embryo showing specially eosinophile leucocytes and a few free 

 eosinophile granules. 



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