Normal Plates of the Development of Necturus maculosus. 



21 



Nose 



Hypo- 

 physis 



Wall of 



nasal 



duct 



consists 



of two 



layers of 



cuboidal 



cells. 



Antero- 



lateral 



wall very 



thin. 

 Lobula 

 tions pro- 

 minent. 

 Epithe- 

 lium of 

 dorsal 

 wall 

 ciliated. 

 Olfactory 

 nerve 

 clearly 

 defined, 



Lies 

 against 

 floor of 



skull 



surroun- 



ded by 



a connec- 



tive 



tissue 

 capsule. 



More 

 lobulated. 



Blood 

 vessels 

 growing 



into it. 



Mouth 



Entire 

 mouth 

 open. 

 Oeso- 

 phagus 

 open. 

 Teeth 

 pro- 

 jecting 



slightly 



into 

 mouth 

 cavity, 



ossified. 



Tongue 

 better 

 devel- 

 oped. 



Glands in stomach well lormed. 

 In anterior half numerous, flask- 

 shaped ; in posterior half tu- 

 bulär. Both kinds unbranchedJ 

 Yolk absorbed in epithelial cells 

 of stomach also in hindgut; 

 midgut cells still heavily laden. 

 Oesophagus open. Liver ex- 

 tends further caudally and dor- 

 sally. Hepatic cords more 

 closely approximated. Yolk 

 partially absorbed. Both dorsal 

 and ventral pancreases larger, 

 showing greater number of 

 tubules. Spleen lies pressed 

 against dorsal wall of body 

 cavity; surrounded by thm 

 layer of connective tissue; 

 shows numerous dividing cells; 

 much connective tissue. 



Enlarged 



transver- 



sely. 



Divided 

 into two 

 portions 



com- 

 posed of 



cells of 

 different 



staining 

 capacity, 



anterior 

 partmore 



deeply 



stained. 



Posterior 



partmore 



lobulated 



and more 



vascular. 



Unicel 

 lular 

 glands in 

 epithe- 

 lium of 

 mouth 



and 



tongue. 



Teeth 



exten- 



ding into 



mouth 



cavity. 



Tongue 



well 

 defined. 



Digestive System, Liver, 

 Pancreas, Spleen 



Gills, Thyroid, 



Thymus, Trachea, 



Lung 



Urino-genital 

 System 



Yolk nearly absorbed in liver. 



Unicellular glands present m 

 mouth, pharynx, Oesophagus 

 and hindgut. Extreme anterior 

 portion of stomach contains no 

 glands. Pyloric glands much 

 branched. Intestine lies in 

 to 5 transversa coils. Cavity of 

 small intestine widely open 

 Muscular walls better develo 

 ped. Epithelium consists of 

 Single layer of long columnar 



yolk-laden cells. Hindgut 

 larger; yolk absorbed; anterior 

 part shows evaginations (glands 

 of Lieberkühn?). Liver lies 

 closely in contact with dorsal 

 wall of coelomic cavity. Yolk 

 all absorbed. Gall bladder very 

 large, surrounded by a layer of 

 connective tissue, epithelium 

 flat. Dorsal pancreas hasgrown 

 caudally and containsso or more 

 tubules ; ventral contains about 

 12 tubules, is about Va size of 

 dorsal. Ducts of both lined with 

 cubical epithelium. 



Trachea longer 

 reaching to caudal 

 region of heart be- 



fore dividing. 

 Lungs longcr, walls 

 better defined, still 

 very thick. Caudal 

 ends detached from 

 intestinal wall ex- 

 cept for Short thin 

 mesentery. Epithe- 

 lium becoming 

 flattened. Mesen- 

 chyma less com- 

 pact. Lungs extend 

 over anterior two 

 thirds of liver later- 



ally to dorso- 

 lateral margins of 

 liver. Posteriorly 

 attached by band 

 of mesenchyma to 

 lateral margins of 

 wall of stomach. 



Gills more pro- 

 minent; filaments 



much branched. 

 All clefts perforate 



excepting fifth. 

 Lateral portion of 



thyroid contains 



small irregulär 



vessels. Pleura 

 proximally layer of 



flattened cells. 

 Some mesenchyma 



between pleura 



and epithelium of 



lungs. 



Pronephros 



reduced in size. 



Tubules cut off 



from coelom ? Duct 



(Ureter) opens into 



cloaca. Meso- 



nephric tubules 



greatly convol- 



uted ; extends from 



g" to 17" somite. 



Bladder comes off 



from cloaca ncar 



point where Ureters 



enter. Sexual 

 cells, a Single row 

 of cells containing 

 large yolk granu- 

 les. Opposite 15" 

 Segment. 



Thymus consists of 

 three spherical 



epithelial patches 

 on each side. Two 

 lie close together 

 opposite posterior 

 portion of ear. 



Anterior largest; 

 posterior much the 

 smallest. Trachea 

 much larger, walls 

 thinner, epithelium 

 flatter. Lungs much 



larger, tapering 

 caudally to end at 

 level of posterior 

 limbs; are attached 

 to intestinal wall 

 and to liver by short 



mesentery. Left 



lung larger than 



right and extends 



further caudad. 



Heart and 

 Blood 

 Vessels 



Glands 

 appear- 

 ing in 

 ventral 

 region, 

 anteriorly 

 and 

 posteri- 

 orly; 

 numerous 

 in lateral 

 portion. 

 Sense 

 Organs 

 more 

 numer- 

 ous. 



Skin 



Skeleton 



Limbs 



Pronephros dege 

 nerating. Extends 

 from middle of 3" 

 Segment to middle 

 of 4", hanging down 

 into body cavity. 

 Duct very small. No 

 openings into body 



cavity discern- 

 ible. Mesonephros 

 extends from 15" to 

 20" Segments. 

 Ducts open into 

 cloaca. Bladder 

 oval, thick-walled, 

 much folded, open- 

 ing into cloaca by 

 Short Urethra, sur- 

 rounded by connec- 

 tive tissue. Sexual 

 glands two rods 

 of large oval cells 

 extending from 13" 

 to 18" Segment, 

 just ventrad of 

 mesonephros. 



Auricles 



nearly same 



size in trans- 



verse 



section. 



Sinus 



venosus 



very large. 



Truncus 



arteriosus 



divided lon- 



gitudinally. 



Trabeculae 



appearing in 



walls of 



auricles. 



Marked 



constriction 



between 



sinus and 



auricles. 



Oval 



cells 

 and sense 

 Organs 

 more 

 numer- 

 ous. 

 Sensory 



hairs 

 evident. 

 Stratum 

 corneum 

 very flat 



cells. 



Stratum 



germina- 



tivum 



two 



layers. 



Skin 

 glands 

 present 

 in ab- 

 dominal 

 region. 

 Stratum 

 corneum 

 a layer of 



squam- 

 ous cells. 

 Basement 

 mem- 

 brane 

 dense. 



Supra-scapula well 



fornied in cartilage 

 extending dorsally to 

 level of spinal cord. 

 Tibia and tibula chon- 

 drified; no tarsals or 

 metatarsals. Ilium and 

 pubis larger. Mesen- 

 chyme around nasal 

 pits. Ossification be- 

 ginning around margin 

 of trabeculae. Para- 

 sphenoids forming as 

 long plates on lower 

 margin of basal plates 

 extending forward to 

 region of eye. Vomer 

 ossified. Frontal ossi- 

 fied at sides and poste 

 riorend. Neural spines 

 beginning to appear 



anteriorly. Indica 

 tions of ossification in 



femur. Ossification 



beginning in neural 



processes and in 



haemal arches. 



Basilar plate continu 

 ous with capsular floor 

 and trabeculae. Jugu- 

 lar foramen formed 

 elongated. Otic pro- 

 cess of quadrate united 

 with otic capsule. 

 Antorbital process 

 further developed. 

 Haemapophyses well 

 developed; not united 

 ventrally. Ossification 

 in phalanges of an- 

 terior limb, also in 

 iliac process. 



Stage 



37 



Limbs 

 better 



de- 

 fined; 

 ante- 

 rior 

 reach 

 ven- 

 trally 



to 

 border 



of 

 yolk. 

 Digits 

 better 

 de- 

 fined 



in 

 both. 



38 



Internasal cartilage 

 connects trabeculae 



anteriorly. Pubic 

 bones united in me- 

 dian line. Tarsals and 

 metatarsals chondri- 

 fied. Palatopterj'goid 

 and sphenoid ossified 



in posterior portion. 



39 



