LATERAL LIP 



Fig. 66. Changes in the shape of the presumptive notochord and the pre- 

 sumptive neural plate during gastrulation. Top left : The presumptive notochord 

 on the surface of the early gastrula. Arrows show direction of movement of 

 cells. Center left: The presumptive notochord has migrated to and over the lip 

 of the blastopore. The dotted line shows that portion of the notochord which 

 has invaginated and formed a part of the roof of the archenteron. Arrows indi- 

 cate direction of movement. Loiver left: Almost all of the presumptive notochord 

 has turned under the lip of the blastopore. It is now in the shape of a long, 

 narrow strip comprising a part of the roof of the archenteron. Top right: Ap- 

 proximate shape of the presumptive neural plate of an early gastrula. Arrows 

 show direction of cell migrations. Center right: The presumptive neural plate has 

 become compressed laterally and stretched along its anteroposterior axis. Lower 

 right: The final shape of the actual neural plate. 



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