Normal Plates of the Development of Nectunis mnculosus. 



15 



Nose 



Hypo- 

 physis 



Mouth 



Digestive System, Liver 

 Pancreas, Spleen 



Nasal tube 

 curvesdorso 



caudally. 



Nasal Organ 



an elongated 



oval. Beco 



ming sepa- 



rated from 



superficial 



ectoderm by 



ingrowing 



mesenchyma 



Condensed 



layer of 



mesenchyma 



around or- 



gan indicates 



beginning 



of fibrous 



capsule. 



Nasal tube 

 deeper. Na 



sal organ 



elongated 

 oval. Con 

 densation of 

 mesenchyma 

 around peri- 



phery of 

 organ niore 



marked. 



Entirely 

 free from 



foregut. 

 Lies close 



against 



infundi- 



bulum. 

 Surroun- 



ded by 



connec- 

 tive tissue 



capsule. 

 Yolk ab- 



sorbed. 

 No trace 



of divi- 

 sion into 

 lobes. No 



cavity. 



Sharply 



defined 



groove 



indicates 



Position 



of mouth. 



Roof and 



floor of 



oral ca- 



vitj'clear- 



ly de- 

 fined but 



cavity 

 liUedwith 



yolk- 



bearing 



cells. 



Dorsal pancreas further 



evaginated. Anlage of 



s])leen as a small mass of 



mesenchymal cells in 



dorsal mesentery of 



stomach. 



Walls of pliarynx consist 

 of one or two layers ot 

 flattened cells excepting 

 posteriorly where still co- 

 'umnar. Oesophagus open. 

 Stomach spindle-shaped, 

 its walls composed of long 

 columnar cells filled with 

 yolk granules ; surroun- 

 ded by two or three layers 

 of densely packed mesen- 

 chymal cells representing 

 the beginnings of its mus- 

 cular walls. Midgut small, 

 dorsal wall fairly well de- 

 fined, ventral wall irregu- 

 lär yolk cells. Cloaca a 

 Wide chamber,yolk nearly 

 absorbed in its dorsal wall. 

 Liver further extended 

 laterally, consists of 15 to 

 20 hepatic cords separated 

 by sinusoids. Cells heav- 

 ily laden with yolk. Gall 

 bladder small but well de- 

 fined. Cystic duct and he- 

 patic duct open in common 

 into the wide ductus cho- 

 ledochus and this opens 

 widely into the intestina. 



Gills, Thyroid, 



Thymus, Trachea, 



Lung 



Gill-bearing arches 



less prominent 

 Gill bars better de- 

 veloped. Gill fila 

 ments recognizablc 



as slight buds. 



Third and fourth 



clefts perforate. 



Tracheal evagina- 



tion deeper, distal 



end dilated, becom 



ing pear-shaped. 



Wall a Single layer 



of cells. 



Posterior portion 

 of thyroid shows 

 beginning of divi- 

 sion into two parts. 

 Tracheal diverti- 

 culum pear-shaped 



lying in mesen- 

 chyma in median 

 line below Oeso- 

 phagus ; cells co- 

 lumnar; yolk being 

 rapidly absorbed. 

 Just anterior to 

 tracheal diverti- 

 culum marked 

 thickening in ven- 

 tral wall of gut. 



Gill bars longer. 

 Gill filaments be- 

 ginning. Second 

 cleft between 



hyoid and first 

 branchial perforate, 



third cleft per- 

 forate, fourth per 

 forate, fifth not per 

 forate. Anlage of 

 thymus as prolifer- 

 ations of epithelium 

 of dorsal portions 

 of gill arches. Tra- 

 cheal evagination 

 longer more dilate'3 

 at distal end. An- 

 lagen of lungs as la- 

 teral diverticula of 

 distal end of tra- 

 chea. Dorsal wall of 



trachea thicker 

 than ventral. 



Urino- 



fenital 

 ystem 



Heart and Blood Vessels 



Proneph- 



rostomic 



openings 



constric- 



ted. 



Pro- 

 nephric 



tubuleslie 

 opposite 



2" or 3" 

 somites. 

 Mesone- 



phros be- 



gins in 9" 

 Segment 



from front 

 and ex- 

 tends to 



17". Best 

 devel- 



oped an- 

 teriorly. 

 Posteri- 

 orly not 

 meta- 

 meric. 



Branchial arches all contain 

 blood vessels. 



Partition separating auricles 

 nearly complete. Truncus 

 arteriosus larger. Primitive 

 aortae large. Hepatic vein 

 very large. Blood vessels 

 present in anterior limb 

 buds. 



Auricle small and nearly 

 spherical; lies just dorso-ce- 

 phalad from ventricle. Ven- 

 tricle turned to the right. Con- 

 striction indicates valves be- 

 tween auricle and ventricle. 

 Sinus venosus verj' large ; it 

 receives ductus Cuvieri, pos- 

 terior cardinals and prone- 

 phric brauch ; also vein for- 

 med by internal and external 

 jugulars. Vitelline vein very 

 large; enters liver. Abdominal 

 vein large, passes through 

 liver, joins hepatic vein and 

 other veins to form hepatic 

 portal sj'stem , then enters 

 sinus venosus. Large vessel 

 on either side. Small vessels 

 in posterior limbs. Vessels 

 around nose and eye; also in 

 pia mater. Dorsal aorta 

 formed. Also subclavian 

 and brachial arteries. 



Skin 



Pigment 

 appear- 

 ing. An- 

 lage of 

 basement 

 mem- 

 brane. 

 Sense Or- 

 gans de- 

 veloping. 



Skeleton 



Skull shows an- 

 läge of trabe- 



culae in Con- 

 densed mesen- 

 chyma. 



Anlage of trabe 

 culae, Meckel's 

 cartilage palato 

 quadrate, basal 



plate, hyoid 

 arch, l", 2" and 



3" branchial 

 arches, first 



basibranchial 

 and faint indi- 



cations of se- 

 cond basibran- 

 chial, also of 

 occipital arches, 

 all in Condensed 



mesenchyma. 

 Mandibular bars 

 separated from 

 each other ven- 

 trally also sepa- 

 rated from basi- 



cranial plates. 

 Quadrate clo- 

 sely applied to 

 Meckel's carti- 

 lage. 



Cartilage appe^ 

 aring around 



outer portion of 

 otic capsule. 



Limbs 



Anterior 

 limbs 

 roject 

 orsally. 

 Posterior 

 imbbuds 

 more pro- 

 minent. 



doi 



Anterior 



limbs 



better de- 



veloped; 



directed 



dorsally. 



Posterior 



limb buds 



slight ele 



vations; 



long axis 



in hori 



zontal 



plane. 



Stage 



