Nnrmal Platcs of the Development of Necturus maculosus. 



23 



Nose 



Hypo- 

 physis 



Moutli 



Digestive System, Liver, 

 Pancreas, Spleen 



Gills, Thyroid, 



Thymus, 

 Trachea, Lung 



Urino-genital 

 System 



Hoart and Blood 

 Vessels 



Skin 



Skeleton 



Limbs 



Stage 



Intestine crosses ab- Lungs reach to 

 dominalcavityö— 7time.s. level of caudal 



Dorsal portion of liver 



connected by narrow 

 band with ventral portion. 

 Hepatic cords closer to- 



gether. Few hepatic 

 ducts. Dorsal and ven- 

 tral pancreases not in 



contact )'et. Tubules 

 more numerous in dorsal. 



Caudal portion of liver 

 occupies over one half of 

 coelomic cavity. Numer- 

 ous hepatic ducts. Dorsal 

 and ventral pancreases in 

 contact. Dorsal much the 

 larger. Spleen longer; 

 compressed dorso - ven 

 trally between intestine 

 and dorsal body wall 

 Connective tissue more 

 abundant. 



end of liver. 



Walls oftrachea 

 and lungs very 



thin; surroun 

 ded by mass of 



mesenchyma. 

 Lungs flattened 



against 

 stomach. Epi 

 thelium thinner; 

 pleural cover- 



ing very thin 



Gills better 

 developed, pig' 

 mented. Fila- 

 ments greatly 

 increased in 

 number. Se- 

 cond, third and 

 fourth gill clefts 

 widely open to 

 exterior; first 

 and fifth imper- 

 forate. 



Under lip 



marked by a 



very deep 



transverse 



groove. No 



Upper lip. 



Tongue 



being cut off 



on ventral 



surface by 



deep lateral 



constric- 



tion. 



Extreme anterior end of 



stomach contains no 

 glands except unicellular. 

 In anterior portion flask- 

 shaped glands are larger 



and more numerous. 

 Middle and posterior por- 

 tion contains branched 

 tubulär glands. Intestinal 



epithelium better de^ 

 fined; still contains yolk 

 granules. Hindgut con- 

 tains branched glands 



Long process of liver 

 extending posterior to 

 gall bladder; another in 

 median line extending 

 over dorsal wall of gut. 



Right lung lies 

 against margin 

 of liver; caudal 

 end in contact 

 with spieen. 



Pronephric ducts 

 smallbut still open 



Mesonephros 

 begins 3 or 4 seg 

 ments behind pro- 

 nephros and ex- 

 tends over about 10 

 Segments. Bladder 

 epithelium short 

 columnar cells, en 

 closed in connec- 

 tive tissue. Walls 



much folded. 

 Sexual glands ex 

 tend from 14" to 

 20" Segments. Yolk 

 granules present in 

 posterior portion. 



Unicellu- 

 lar gland 

 and sense 

 Organs 

 very nu- 

 merous. 

 Sensory 



hairs 

 project- 

 ing bey- 



ond 

 surface. 



Ossification be- 



ginning in 

 haemal arches. 



Ossification 

 well defined in 

 haemal arches. 



Pericardium well defined, 

 very thin, detached from 

 muscular wall. Auricles 

 widely in communication 

 with each other. Blood 

 passes into ventricle by 

 Single opening on left 

 side. Valves present in 

 this opening. Semilunar 

 valves between ventricle 

 and Conus appear as ex- 

 tended proliferations of 

 wall. Valves also present 

 between conus and 

 truncus. 



Mucous 

 glands 

 larger, 

 abundant, 

 none on 

 ventral 

 surface. 

 Unicellu- 

 lar glands 

 more nu- 



40 



Limbs 



longer, 



pigmen- 



ted, both 



pairs 



func- 



tional. 



Four 



digits 



well 



defined 



on each. 



All the carti 

 lages of carpus 

 andtarsusmeta 



carpus and 

 metatarsus and 



phalanges 

 formed. Middle 



portion of 

 Meckel's carti- 

 lagesurrounded 

 by bone. Pre- 

 maxillae and 

 frontals well 

 ossified. Carti- 

 läge appearing 



in center of 



body of verte- 



brae. 



42 



43 



