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NEURULATION AND EARLY ORGANOGENY 



Early development of caudal structures. {Top, left) Posterior view of late 

 neurula. {Top, right) Enlargement of illustration at top, left. {Bottom) Sagittal 

 section through the posterior end; (dashes) nervous, {circles) entoblast (pre- 

 sumptive endoderm), {crosses) notochord, {dots) mesenchyme (presumptive 

 mesoderm). (Pasteels, Jean, 1943, Fermeture du blastopore, anus et intestin 

 caudal chez les Amphibiens Anoures, Acta Neerland. morphoL, 5:11.) 



gether, this sense plate remains distinct (i.e., the sides do not become 

 fused as do the neural folds), but its posterior limits merge with the 

 outer margins of the lateral neural folds even after the fusion of the 

 latter structures. These sense plates will give rise to the mandibular 

 (first visceral) arches, lens of the eyes, nasal placodes, and oral suckers. 

 The ridges are formed largely from mesoderm and will give rise to 

 parts of the jaw apparatus. The superficial suckers are paired larval 

 organs that take the shape of an inverted "U." They become glandu- 

 lar and form a mucous secretion which the larva uses to adhere to 

 objects after hatching. 



The anterior median level of the sense plate will shortly develop a 

 vertical groove, the stomodeal cleft, which separates the two mandib- 

 ular ridges (arches) or primordia of the right and left sides of the 



