II.] 



THE AMNION. 

 Fig. 11. 



•i.5 



Diagrammatic longitudinal section through the pos- 



TERIOB END OF AN EMBKTO BiRD, AT THE TIME OP THE 

 FORMATION OF THE AlLANTOIS. 



ep. epiblast ; Sp.c. spinal canal ; ch. notoohord ; n.o. neurentei-ic 

 canal ; hy. hypoblast ; p.a.g. postanal gut ; pr. remains of 

 primitive streak folded in on the ventral side ; al. allantois ; 

 me. mesoblast ; an. point where anus will be formed ; p.c. 

 perivisceral cavity ; am. amnion ; so. somatopleure ; sp. 

 splanohnopleure. 



Each fold, of course, necessarily consists of two 

 limbs, both limbs consisting of epiblast and a very thin 

 layer of mesoblast ; but in one hmb the epiblast looks 

 towards the embryo, while in the other it looks away 

 from it. The space between the two limbs of the fold, 

 as can easily be seen in Figs. 9 and 11, is really part 

 of the space between the somatopleure and splanoh- 

 nopleure ; it is therefore continuous with the general 

 space, part "of which afterwards becomes the pleuro- 

 peritoneal cavity of the body, shaded with dots in 

 figure 9 and marked {pp). It is thus possible to 

 pass from the cavity between the two limbs of each 



