Normal Plates ol the Development of Necturus maculosus. 



Segmentation 

 cavity 



Blastopore. Anus 



Archenteron. Enteron. 

 Mesoderm. Chorda 



Neurenteric 

 canal 



Nervous System. 

 Optic vesicles. Somites 



Stage 



Präsent , large ; roof 

 Single layer thick. 



Large, roof in nart two 

 layers thick. 



Segmentation cavity 



larger, roof in part 



two layers thick. 



Segmentation cavity 



large, roof in part 



three layers thick. 



Roof thinner , four 



layers around peri- 



phery, single layer in 



center. 



Well formed. 



Smaller. 

 Smaller. 



Quite small. 



Very small. 



Very small. 



Very small. 

 Not present (?). 



Small, well defined. 

 (?) 



Present as large spaces 

 among yolk cells. 



Crescentic fissure on 

 ventro-lateral portion of 

 egg- 



Horse-shoe-shaped. 



Circular. 



Small, circular, yolk plug 

 externally visible. 



Very small, circular, yolk 

 plug externally visible. 



Elongated dorso - ven- 

 trally; yolk plug not ex- 

 ternally visible. 



Yolk plug not present. 



Archenteron just beginning. 



Archenteron extends over about 20" 

 Peristomal mesoblast present at dorsal 

 lip of blastopore. 



Archenteron extends over about 45°. 



Dorsal wall posteriorly two layers. 



Peristomal mesoblast well defined in 



ventral lip of blastopore. 



Archenteron nearly complete; dorsal 

 wall two layers anteriorly. Meso- 

 blast around entire blastopore. An- 

 lage of chorda. 



Archenteron very nearly complete; 

 Single layer in mid-longitudinal axis; 

 this layer is beginning of chorda 

 Paraxial mesoblast co-extensive with 

 chorda. 



Lateral walls of enteron three layers 



Somatic and splanchnic layers well 



defined. Chorda well defined in head 



region. 



Enteron single-layered dorsal wall; 

 mesoblast extends ventrally over one- 

 half of egg. Chorda narrower, thicker. 



Walls of enteron as above. Meso 



blast extends to ventral portion of 



egg; well defined coelom. Chorda 



anteriorly a rod of cells. 



Chorda oval or round in cross section 



througliout head and trunk regions. 



undifferentiated in tail. 



Present. 



Present. 



Present, 



small. 



Tubulär. 



Small canal 



VVidely 

 open. 



Anus perforate. 



Enteron as above. Mesoblast over Closed (?). 

 ventral surface of egg. Chorda well 

 defined in head and trunk regions. 



Broad neural plate of thicke 



ned ectoblast; shallow neu 



ral groove. 



Low neural ridges present, 

 deep neural groove. 



Higher neural ridges, deep 

 neural groove. 



Prominent neural folds ap- 



proaching each other, deep 



neural groove. 



High neural ridges approxi 



mating, but nowhere in 



contact. 



Neural ridges meet in ante- 

 rior head region. Beginning 

 of optfc vesicles. 



Neural ridges not closed in 

 head region but coalesced 

 in posterior trunk region and 

 in tail. Optic vesicles better 

 defined. 



Neural folds closed through- 

 out entire length of embryo. 

 Optic vesicles prominent, 

 outer wall single layer of 

 cells. Three or four somites 



10 



13 



14 



16 



17 



NormentafelD lur Entwicklungsgeschichte der Wirbeltiere. XI. 



