30 



K-MITSUKTJRI. 



îillantoic lobes become closely applied agjiiiist the mosoblii^t of tbe 

 connection but nre permanently sepnrate from on<'h other. The 

 epiblast of both the nmnion and the serons envelope consists of tAvo 

 layers of cells. The inner la\er of the former and the outer Inver of 

 the latter consist of very much flattened cells with hirge nuclei — 

 which, in the case of the serous envelope at least, nre much laru-erand 

 stained deeper than those of the second layei-. It is the cells of the 

 outer layer which become specially laro'e in the reo-ion of the placeiitn. 

 The second or underlying layer consists of cubical cells which in 

 some places may be present in more than one layer. It is this inner 

 second layer alone that forms the sero-;nnriiotic connection, the outer 

 taking no part in it. As reçfards the allantois, the outer limb is 

 generally much thicker than the iiiner litnb and has many more blood- 

 vessels distributed in it. The thickness of the allantoic walls is 

 crossed in all directions by slender spindle-shaped cells. 



Fig-. 79 corresponds to the line 2-2 in Fig. 77 just through 

 the anofle of the bend w^hich the sero-ainniotic connection makes. 

 The sero-araniotic connection goes here on one side to the amnion 

 and on the other to the remnant of the posterior tube of the amnion, 

 which, being now reduced to a thick compressed and somewhat con- 

 voluted sti-ing of cells, shows in section as lobated cell-masses. 



Fig. SO corresponds to the line 3-3 in Fig. 77. The sero- 

 amniotic connection is no longer continuous with the serous envelope 

 but goes to the remnant of the posteri<n' tube of the amnion. To the 

 rigfht of the sero-amniotic connection, the two lobes of the allantois 

 meet but are not fused. This is the section of the conical white 

 streak that stretches over tlie dorsal region of the embryo and (V)rres- 

 ponds to the simple incision of the allantois given in Fig. 12 (PI. Tl.). 



In a few more sections, the sero-amniotic connection disappears. 

 The two lobes of the allantois, however, keep separate and meet in 



