Gastrulation continues throughout all sub-divisions of this stage and:

MS: Tissue at the posterior end of the primitive streak bulges into the proamniotic cavity and forms the posterior amniotic fold.  

LSOB: In the mesoderm of the posterior amniotic fold small cavities coalesce to form a single cavity, the exocoelom.

LSEB: The allantoic bud first appears, gastrulation continues and the node becomes visible.

7 dpc (range 6.5-7.5)  
Downs & Davies  MS-LS  midstreak to late streak  
Witschi Stage 12 (rat)  
Carnegie Stage 8 (human - stage table)

Scale bar in microns.