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HfROTA; OX THE SERO-AMXIOTIC rOXXEOTfOX, 



Diaé. 10. 



Interall, Septum 



Part of a Cross-Section 

 of the Albumen-Sac. 



As fasf :is the albiinien is absorbed the primary interallantoic 

 septum widens itself inwards at the expense of the inner limbs of the 



two allantoic lobes, which progres- 

 sively coalesce with ench other as the 

 albumen diminishes nnd the albu- 

 men-sac contracts in volume. A 

 reference to Diag. 10 will make 

 what is meant clear. Suppoae the 

 outer limit of the albumen-sac to be 

 the line 1-1. It is bounded by the 

 two lobes of the allantois, and the area 

 witliin which they overlap (a b) is the internllantoic septum. If now 

 the albumen-sac decreased in diameter to the line 2-2, the inter- 

 allantoic septum would then be widened to the point c, by the coales- 

 cence of the inner limlîs of the two allantoic lobes. Thus the decrease 

 of albumen will make the width of the interallantoic septum increase 

 and the diameter of the albumen-sac grow smaller. Hence, the 

 line along which the interallantoic septum is (continuous with the 

 inner allantoic limb (appearing as the points b, c, d, in a cross-section 

 like Diag. 10), will always lie on the albumen-sac. The line AA 

 represented in Figs. 51-56 is, in fact, this line. The i-elation of the 

 inner edge of the inter:dlant(nc septum (DKG) in Figs. 17 and LS 

 to the cave-like diverticulum of the albumen-sac will make this evi- 

 dent. These changes are accompanied by gradual enlargement of the 

 amniotic cavity and gradual decrease of the yolk. Tiie stage in 

 which these conditions are observed is given in Figs. '22-'2b, of which 

 the first two re])resent surface views of the foeral membranes frcnn 

 two opposite sides; and the last two give theii* outlines. The letters 

 as far as possible refer to the same parts as in Figs. 14-lN. Tlie 

 bloodvessels first become visible in passing from beneath the amnion 



