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vessel, which is seen dividing, being the vein. The number and nature 

 of the blood vessels here reported agrees with portion of Meter's 

 statement that 'sometimes three arteries and two veins are found, while 

 in other cases one vein and two arteries are present". From this 

 point outward the blood vessels divide and sub-divide until at the 

 distal pole the resulting branches are mere capillaries and blood spaces 

 without definite walls. 



Throughout the distal three-fourths {^U) of the umbilical vesicle 

 the zona media contains numerous evaginations from the entodermal 



Fig. 3. Transverse section of yolk sac at the level of the pedicle. Two vitelline 

 arteries are seen to the right of the figure ; the vitelline vein is seen dividing at the 

 left. The entodermal wall of the central lumen shows a cell filled with erythroblasts. 

 M mesoderm ; E entoderm ; m mesothelium ; e endothelium of blood vessel. Stain, 

 hematoxylin and eosin ; thickness, 10 micra ; photomicrograph, )x( 240. 



wall ; these are the "crypts" mentioned by Selenka and the "glands" 

 described by Graf Spee. Though Paladino does not mention the pre- 

 sence of such glands, he nevertheless compares the yolk sac wall to 

 „glandular tissue". Toward the distal pole these glands become pro- 

 gressively more numerous and more closely packed (Fig. 2). Study 

 of serial sections reveals that the glands may be mere tubes of ap- 



