i6 



Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 



Stage 



Series 



Length 



30 



140 Trans. 



144 Sag. 



145 Front. 



31 



147 Trans. 



156 Sag. 



157 Front. 



32 



17 mm 



18 mm 



Age 



Body Form 



38 days 



40 days 

 20 hrs. 



159 Trans. 



160 Sag. 

 162 Front. 



19 mm 



43 days 



33 



164 Trans. 



173 Sag. 



174 Front. 



20 mm 



Somites 



Horizontal 



section shows 



40 — 42 myo- 



tomes. 



Trunk and tail 

 slightly concave in 

 profile. Cervical 

 flexure still präsent. 



Cephalic flexure 

 less marked. Tail 

 very wide dorso- 



ventrally. Yolk 



more elongated, 

 convex on ventral 



surface, slightly 

 concave on dorsal 

 margin. Pigmen- 

 tation more pro- 

 nounced. Mandi- 

 bular arches coa- 

 lesced. Boundaries 

 of other arches no 

 longer visible. 



46 days 

 2 hrs. 



Horizontal 



section shows 



44 — 46 myo- 



tomes. 



Notochord 



Nervous System 



Yolk not absorbed 

 in anterior end. Va- 

 cuolated through- 

 out. Mesenchyma 

 between anterior 



end and hypo- 

 physis. Posteriorly 

 rests against neu- 

 ral tube. Not seg- 

 mented. Begin- 

 nings of neural 

 arches in carti- 

 lages. 



Eye 



Plexuses much less mar- 

 ked. Anterior end of 

 brain formed by hemi-| 

 spheres. Paraphysis well, 

 developed; plexus ex- 

 tends into lateral ventri- 

 cles and diencephalon. 

 Lamina terminalis thick. 

 Anterior commissure well 

 defined, also commissura: 

 habenularis. Lamina cere- 



bellaris recognizable. 

 Ganglion of trigeminal 

 divided into two parts. 

 Spinal cord rounder ; canal . 

 shorter dorso-ventrally. 

 Ganglia very large ; nerve 

 roots well developed; 

 nerve fibers appearing in 

 ventral nerve roots. An- 

 lage of pia mater. 



Ear 



Horizontal 



section shows 



48 — 50 myo- 



tomes. 



Optic cup flattened 

 laterally, surrounded, 

 except on outer sur- 

 face, by Condensed 

 mesenchyma. Retina 



divided into two 

 layers; contains some 

 pigment. Anlage of iris 

 present. Optic stalk 

 smaller , cavity very 

 small. Lens larger, 

 spherical , inner wall 

 fiUs cavitj- except nar- 

 row cleft. Anterior! 

 wall a Single layer of 

 cells. Lens fibers for- 

 ming. 



Dorso-ventrally 

 compressed. Yolk 

 granules still pre- 

 sent in peripheral 



portion. Neural 

 arches better de- 

 veloped anteriorly. 



Ear more exten- 

 ded antero-pos- 

 teriorly. Utri- 

 culo-saccular 

 partition begin- 

 ning. Ductus 

 endolympha- 

 ticus extends 

 over lateral mar- 

 gins of meduUa 

 toward median 

 line; dilated at 



distal end to 

 form Saccus. An- 

 lagen of lagena 

 and semicircu- 

 lar canals. Peri- 

 otic capsule for- 

 ming in Con- 

 densed mesen- 

 chyma. 



Pigment increased in 

 posterior layer of optic 



Spinal cord shows well 



defined layer of fibers ^„.^i^...^. .„j^. -. -t--- -^^ » — 



entirely around it. Layer cup. Retina in three appearonexter 

 is thicker in ventral half, ' r^_.:„ „^„ii. „_i . — »_„i „i^. 



Periotic capsule 

 beginning to 



thin on dorsal portion. 

 Transverse diameter of 

 cord greater than dorso- 

 ventral. Around central 

 canal a layer of cells 



radiates from canal. 



Nerve fibers numerous in 



ventral roots of spinal 



nerves. 



Cephalic flexure 

 reduced. Axis of 

 tail coincides ex- 

 actly with axis of 



trunk. Yolk re- 

 duced dorso - ven 

 trally, more elonga 

 ted, more pointed 



at anterior end 

 Dorsal and ventral 



surfaces convex 

 Pigment Ijetter de- 

 veloped. 



Anterior end close 



to hypophysis; 



slightly knobbed. 



Portion anterior to 



heart much smaller 



than remaining 



portion; greatly 



enlarged at level of 



anterior margin of 



yolk. Segmenta- 



tion well marked 



excepting in caudal 



portion. Neural 



arches in anterior 



trunk region extend 



dorsally to level of 



middle of spinal 



cord. 



layers. Optic stalk 

 still presents minute 

 lumen; fibers bedn- 

 ning to be formed in 

 its walls. Lens spheri- 

 cal ; posterior wall fills 

 entire cavity; epithe- 

 lium a Single layer of 

 cuboidal cells 



nai ventral side 

 of ear. 



Three la}xrs well defined 

 in walls of fore brain 

 Epiphysis a large oval 

 vesicie with thin dorsal 

 wall ; communication into 

 third ventricie nearty cut 

 off. Walls of paraphysis 

 irregulär. Choroid plexus 1 

 extending into ventricles. 

 Lateral lobes of infundi- 

 bulum extended to level 

 of mid brain. Cerebral 

 peduncles formed in 

 ventro - lateral walls of 

 mesencephalon. 



Horizontal 



section shows 



some 50—55 



myotomes. In 



anterior trunk 



region muscle 



plate wider, 



extending ven- 



trally over 



dorso-lateral 



margins of yolk. 



Septa thicker. 



Two thirds of 



myoblast fibril 



lated. 



Optic cup flattened 

 laterally. Ora serrata 

 better defined. Begin- 

 nings of iris and ciliary 

 body. Fibers in optic 

 nerve better devel- 

 oped. Lens cells ar 

 ranged concentrically; 

 jfibers numerous ; mar- 

 ked chromatolysis in 

 central portion. 



Periotic capsule 

 extends further 

 dorso-mesially. 



At level of anterior 

 limbs notochord is 

 much larger than 

 spinal cord, at level 

 of posterior limbs 

 much smaller. Yolk 

 not quite absorbed 

 around periphery. 

 Neural arches m 

 anterior trunk re- 

 gion extend dorsally 

 to top of spinal 

 cord, not united; 

 beginning in poste- 

 rior trunk region ; 

 in anterior caudal 

 region indicated in 

 procartilage. 



Olfactory nerve connec- 

 ted with fibrous areas in 

 hemispheres. 



Layers of retina well 

 defined ; pigment more 

 dense. Lumen of optic 

 stalk obliterated near 



brain wall; exceed- 

 ingly minute distally; 

 fibers more numerous. 

 In Center of lens nuclei 



have nearly disap- 

 peared. Epithelium of 

 lens a layer of cubo- 

 idal cells. Fibers well 

 defined, more nume- 

 rous, concentricallj' 

 arranged. Eye mus- 

 cles better developed. 



Utriculo-saccu- 

 lar partition ex- 

 tends well into 

 vesicie. Anterior 



semicircular 

 canal better de- 

 veloped than the 

 others. Macula 

 acustica sacculi 

 well defined. 

 Periotic capsule 

 surrounds ear 

 except mesial 

 surface. 



