Normal Plates of the Development of Necturus maculosus. 



19 



Nose 



Hypo- 

 pliysis 



Organ 



longer, 



becoming 



slightly 



concave an 



ventral sur- 



face. Further 



indications 



of lobula- 



tions. 



Nasal duct 



opens into 



Pharynx on 



one side. 



Connective 



tissue and 



bloodvessels 



extend into 



ventral wall 



giving it a 



much lobul- 



ated ap- 



pearance; 



dorsal 



wall also 



slightly 



lobulated. 



Nasal tubes 



open into 



Pharynx on 



both sides. 



Mouth Digestive System, Liver, 

 Pancreas, Spleen 



Gills, Thyroid, 



Thymus, 

 Trachea, Lung 



Mouth 



cavity still 



closed. 



Mouth 

 broken 

 through. 



Posterior 

 median 

 portion of 

 cavity still 

 contains 

 yolk-bearing 

 cells. Papu- 

 lae of teeth 

 formed. 



Glands better defined. 

 Nu dilTerentiation into 



pyloric and cardiac 

 glands. Liver roughly 

 triangulär in section, has 

 extended cautially. Uall 

 bladder still small, lining 

 still a Single layer of co- 

 lumnar cells filled with 

 yolk granules. Hepatic 

 cords more definite owing 

 to absorption of yolk. 

 Dorsal pancreas lumen 

 and duct snialler. Se- 

 veral small tubulär eva- 

 ginations Coming off from 

 it. Ventral pancreas lo- 

 bules not distinct. Spleen 

 an elongated massot cells 

 compressed dorso • ven- 

 trally Ij'ing in mesentery 

 just above stomach. 



Dorsal pancreas smaller, 

 tubules fewer. Yolk ab- 

 sorbed in cells. Pro 

 zymogen granules ab 

 undant. 



Posterior portion of liver 

 has extended dorsally to 

 level of posterior portion 

 of stomach; contains few 

 bile ducts. Cells loaded 

 with 3'olk. Tubules much 

 more compact; sinusoids 

 narrower, changing to 

 capillaries. Gall bladder 

 larger, cells in wall low 

 columnar or cuboidal, 

 free from yolk. Dorsal 



pancreas 6 — 8 tubules. 

 Ventral as above. Spleen 



larger, more vascular. 



Gills further devel- 



oped showing 



greater numl)er of 



filaments. Gill 



clefts open be- 



tween hyoid and 



first branchial 



arches, between 



first and second 



archesand between 



second and third 



branchial arches 



but fifth cleft not 



open. Lumina of 



lungs still larger. 



Tips of lungs reach 



anterior margin of 



liver. 



Trachea larger and 



longer. Lungs 

 longer, caudal ends 

 behmd heart, over 

 anterior portion of 

 liver. Walls better 

 defined, epithelium 



cuboidal. Yolk 

 nearly all absorbed. 



Trachea smaller, 

 lining layer of cells 

 flat. Lungs much 

 farther distended 

 laterally, extending 

 to extreme lateral 



margins of the 

 liver. Pleura con- 

 sist of layer of 

 closely apposed 

 cuboidal cells. 



Urino- 

 genital 

 System 



Glome- 



ruli well 



defined. 



Tubules 



very 



much 



coiled. 



Pro- 

 nephric 

 tuljules 

 reduced 



Heart and 

 Blood Vessels 



Auricles further 



developed. 

 Cavity of ven- 



tricle large, 

 walls thin,many 



trabeculae. 

 Walls oftruncus 

 much thicker 

 than those of 

 Conus. Valves 

 beginning to be 

 formed between 

 Conus and ven- 

 tricle ; also be- 

 tween Conus 

 and truncus. 



Skin 



Cells of 

 Stratum 

 germina- 



tivum 



flattened. 



Glands and 



sense organs 



more 



numerous. 



Skeleton 



Glands 



larger; sunk 



below level 



of epider- 



mis; contain 



lumen. Cells 



of Stratum 



germina- 



tivum 

 elongated 

 flattened. 



Procartilage present in Anterior 



pclvic girdle and in limbs 

 feniur. Ossification in project 

 side walls of brain case, caudo- 

 also in base. Anlage of vcntrally; 

 dentale as ossified plate digits 

 on external surface of plainly 

 Meckel's cartilage. Be- defined. 

 ginning of angulare as[ Posterior 

 thin plate of bone. Indi- limbbuds 

 cations of mento-mandi- project 

 bulare. Ossification be- caudad. 

 ginning in premaxilla and 

 in quadrate. 



Limbs 



Occipital arch growing up 

 from sides of notochora ; 

 below uniting posterior 



ends of parachordals. 

 Parachordals fused with 

 basal plates. Traceoftra- 

 becular crest to which 

 process of quadrate is 

 attached. Short otic pro- 

 cess fused with otic cap- 

 sule. Coracoid process 

 extends nearly to ventral 

 margin of liver; scapular 

 extends to upper margin 

 of notochord. Humerus 



larger; glenoid cavity 

 very deep. Ulna and ra- 

 dius chondrified. Anlage 

 of carpals and metacar- 

 pals. Pelvic girdle chon- 

 drified ; consists of dorsal 

 iliac portion and ventral 

 pubic portion. Femur 

 chondrified; anlagen of 

 tibia and fibula. 



Floor of otic capsule 

 nearly complete. Ossifi- 

 cation beginning in para- 

 sphenoid also in parle 

 tals and frontajs. Anlage 

 of vomer. Neural arches 



developed throughout 

 body; meet dorsal!}' in 

 trunk, not in tail. Haem- 

 apophyses appearing in 

 anterior portion of tail. 

 Ossification beginning in 

 neural arches. Bone well 

 developed around 



Centers of vertebrae. 

 Traces of ossification in 



scapula and humerus. 



3* 



