II.] THE EMBRYONIC APPENDAGES. 31 



whole space between the splanchnopleure and the somatopleure, 

 it is evident that a way is open for the allantois to extend from 

 its present position into the space between the two limbs of the 

 amniotic fold af. 



Ej also a longitudinal section, represents a stage still farther 

 advanced. Both splanchnic and somatic stalks are much nar- 

 rowed, especially the former, the cavity of the alimentary canal 

 being now connected with the cavity of the yolk-sack by a mere 

 canal. The folds of the amnion are spreading over the top of 

 the embryo and nearly meet. Each fold consists of two walls 

 or limbs, the space between which (dotted) is as before merely 

 a part of the space between the somatopleure and splanchno- 

 pleure. Between these arched amniotic folds and the body of 

 the embryo is a space not as yet entirely closed in. 



F represents on a different scale a transverse section of E 

 taken through the middle of the splanchnic stalk. The dark ring 

 in the body of the embryo shews the position of the neural canal, 

 below which is a black spot, marking the notochord. On either 

 side of the notochord the divergence of somatopleure and splanch- 

 nopleure is obvious. The splanchnopleure, more or less thick- 

 ened, is somewhat bent in towards the middle line, but the two 

 sides do not unite, the alimentary canal being as yet open below 

 at this spot ; after converging somewhat they diverge again and 

 run outwards over the yolk. The somatopleure, folded in to 

 some extent to form the body- walls, soon bends outwards again, 

 and is almost immediately raised up into the lateral folds of the 

 amnion af. The continuity of the pleuroperitoneal cavity within 

 the body with the interior of the amniotic fold outside the body 

 is evident ; both cavities are dotted. 



(7, which corresponds to D at a later stage, is introduced to 

 shew the manner in which the allantois, now a distinctly hollow 

 body, whose cavity is continuous with that of the alimentary 

 canal, becomes directed towards the amniotic fold. 



In H a longitudinal, and / a transverse section of later date, 

 great changes have taken place. The several folds of the amnion 

 have met and coalesced above the body of the embryo. The inner 

 limbs of the several folds have united into a single membrane (a), 

 which encloses a space (ae or ac) round the embryo. This mem- 



