53 



resenblin.rr a r>trinp If beads soTewhat coiled, 



V.ith this seraration a-d rollinp ar-art, the rrp:ularity 

 of arranger-pnt of the cells in the seg^entinfT egg is lost, and 

 the stager, frc" this noint on become '^ore and more irregular 

 v/ith each successive division u^ to the time when the re- 

 ad.iustinent tal;es -ilace v;hich is the beginning of the fnr- 

 nation of the free-sv/irr?ing e-: bryo. 



It is possible t-- distinguish, during these early 

 cleavage stages, a layer of ectosarc around each individual 

 blastomere. Later as the cells increase iri nuTber and be- 

 come smaller, the ectcsarc covering beco-r-es less "O'^soicu- 

 ous and finally is lost frcr sight entirely. 



After a"" interval of about one half an hour, the fourth 

 segmentation begins. The divisions of the different cells 

 no longer tahe nlace sirultaneously; sere occur a few minutes 

 before others, but all are cornle'ued within a coTDaratively 

 short tin:e. So&'ar a- the cleavage itself is concerned, it 

 is ntill ecual and regular, but the arrangement of the blasto- 

 Tieres is no longer regular or definite. They annarertl> 



