PRE-GASTRULATION STAGES 



105 



of the effective forces that make for a morphogenetic integration of 

 the dynamic functions of the single cells into a cooperative unity." 

 Embryologists have long been in search of a controlling supercellular 

 physical force which might explain at least the initiation of the move- 

 ments leading to gastrulation. This surface coat of Holtfreter may well 

 be that controlling and integrating force. He suggests further that 

 probably all of the non-adhesive epithelial linings of the larva can 

 be traced back to this original surface coat. 



(kjina pipiens) 



(stags identified by number) 



Blastula to tail bud stages. (AP) Animal pole. (BR 1) First branchial cleft. 

 (BR 2) Second branchial cleft. (BR 4) Fourth branchial cleft. (DLBP) Dorsal 

 blastopore lip. (GA) Gill anlage. (GP) Gill plate. (GR) Germ ring. (HMCL) 

 Hyomandibular cleft. (LNF) Lateral neural fold. (MP) Medullary plate. (MY) 

 Myotome. (NG) Neural groove. (OP) Optic vesicle. (OS) Oral sucker. (PRN) 

 Pronephric region. (SP) Sense plate. (TNF) Transverse neural fold. (VP) 

 Vegetal pole. (VLBP) Ventral blastopore lip. (YP) Yolk plug. 



