Normal Plates of the Development of Necturus maculosus. 



13 



Nose 



Hypophysis 



Mouth 



Digestive 

 Sj'stem , 

 Liver, 



Pancrcas, 

 Spleen 



Gills, Thyroid, Thymus, 

 Trachea, Lung 



Urino-genital 

 System 



Heart and Blood 

 Vessels 



Skin 



Ske- 

 leton 



Limbs 



Stage 



Disk-like 

 depression 

 on surface 

 deeper. Na- 

 sal epithe- 

 lium thicUer, 

 separated 

 from fore- 

 biain by thin 

 layer of 

 mesen- 

 chyma. 



Invagination 

 deeper, cup- 

 like. In free 

 ends of cells 

 forming 



bottom of 

 cup, yolk is 

 entirely ab- 

 sorbed leav- 



ing clear 

 Zone. 



Nasal pit for- 

 med ; organ 

 oval in out- 

 line. 



An oval loosely 

 arranged mass 

 of cells contain- 



ing irregulär 

 cavities.Antero- 

 ventral wall 

 thinner than 

 dorsal. Yolk 

 not absorbed. 



Gill bearing arches recog- 

 nizable as divisions in a 

 common enlargenient from 

 which they develop. An- 

 lage of external gills as 

 slight proliferations. An 

 läge of trachea as longitu- 

 dinal groove in median line 

 of thickened ventral wall 

 of Oesophagus. Gill clefts 

 indicated by deep evagin 

 ations of pharyngeal and 

 corresponding mvagination 

 of surface ectoderm. Noecto- 

 dermal invagination bet- 

 ween fourth and fifth arches. 



Gill bearing arches better 

 developed. Ectodermal in- 

 vagination between fourth 

 and fifth arches. Tracheal 

 groove deeper; wall a single 

 layer of columnar cells. 



Pronephricduct 



much coiled at 



anterior end; 



sanie caliber 



throughout ; 



widely open 



anteriorly into 



coelom; poste- 



riorly open into 



cloaca. No 



trace of meso- 



nephros. 



Epithelium 

 of mouth 

 shovvs as 

 columnar 

 layer of 

 cells, al- 

 though yolk 

 is not absor- 

 bed in mouth 

 cavity. 



Nasal pit a 

 short cylin 

 der. Epithe- 

 lium thicker. 

 Clear Zone at 

 free ends of 

 cells broa- 

 der 



An oval mass of 

 cells closely 



applied to in- 

 tundibulum. 



Contains cavity. 



Capsule begin- 



ning to be for- 

 med. 



Anlage of 

 gall blad- 

 der. An- 

 lage of 

 dorsal 

 pancreas. 



Heart somewhat twisted. 

 Endothelium and meso- 

 thclium defined. Blood 

 vessels prescnt in ante- 

 rior branchial arches. 

 Truncus arteriosus for- 



med. Beginnings of 

 vitelline veins as irre- 

 gulat Spaces on ventral 

 surface of yolk. Anterior 

 and posterior cardinal 

 veins forming. Blood 

 capillaries appearing over 

 surface of yolk. No blood 

 vessels in tail. 



Gill bearinCT arches better 

 defined. Gill bars pro- 

 minent but no gill fila 

 ments. Pharyngeal portion 

 of gill clefts extends two 

 thirds distance to exterior, 

 meeting ectodermal invagin- 

 ations. Walls of clefts 

 closely apposed. 



Thyroid extends backward 

 to anterior wall of pericar- 

 dium. Tracheal evagination 

 deeper, tubulär. 



Generally 

 two layers. 



Cuticular 

 margin well 

 developed. 

 Shows Stra- 

 tum corneum 

 and Stratum 



germina- 

 tivum, each 



a Single 

 layer of cells. 

 Many large 



oval cells 



(mucous, 



"Leydig" 

 cells). 



Heart placed transver- 

 sely. Large abdominal 

 vein formed communica 

 ting with sinus venosus. 



Pronephric tu- 

 bules still wi- 

 dely open into 

 coelom. Poste- 

 rior portion nar 

 rower than ante 

 rior. No meso- 

 nephros. 



Heart S-shaped, twisted 

 Auricular portion tubu- 

 lär. Ventricie constricted 

 where itopens intoconus. 

 Conus and truncus not 

 differentiated. Endothe- 

 lium of ventricie and of 

 pericardial cavity a single 

 layer of flattened cells. 

 Anterior and posterior 

 cardinal veins formed. 

 Large abdominal vein 

 running through the liver 

 Beginning of portal cir- 

 culation. 



Cuticular 

 margin 

 thicker. An- 

 lage of late- 

 ral line 

 Organs. 



Anlageof 



anterior 



limbs 



visible. 



23 



24 



Anterior 

 limbs 

 more 

 prom- 

 inent. 

 Posterior 

 limb buds 

 just dis- 

 cernible. 



25 



36 



