12 



Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 



Stage 



Series 



23 



111 Trans. 



112 Sag. 



113 Front. 



24 



116 Trans. 



117 Front. 



25 



118 Trans. 



119 Sag. 



Length 



12 mm 



26 



120 Trans. 



125 Sag. 



126 Front. 



Age 



Body-form 



24 days 

 22 hrs. 



26 days 



28 days 

 2 hrs. 



13 mm 



Head more 

 elevated. Optic 



vesicies pro- 

 minent. Embryo 

 less curved ven- 

 trally and late- 

 rally. Tail end 

 enlarged, be- 

 Coming free 

 from yolk. Yolk 

 becoming oval 



in outline. 



Markedcephalic 



flexure. 



Outline of body 



straighter. 

 Anterior limb 



buds indicated. 

 Yolk pear- 



shaped. Heart 

 prominent. 



Embryo less 

 curved dorso- 

 ventrally and 

 laterally. Head 

 end free to an- 

 läge of heart 

 Tail end pro- 

 jects further 

 from yolk. 

 Markedcephalic 

 flexure. Ends 

 of mandibular 



arches near 

 median line but 

 still separate. 

 Yolk changed 

 from oval form 

 to pear-shaped, 

 small end an- 

 terior. Capil- 

 laries appearing 

 in yolk. 



Somites 



Externally 23 



to 24 pairs of 



myotomes. 



Muscle plate 



much wider 



laterally, ex- 



tends further 



ventrally. Myo- 



coele small. 



Notochord 



Sheath well defined, 

 a Single layer of cells. 

 Vacuolated through- 

 out excepting a small 

 portion at posterior 

 end. Hypochorda well 

 defined. 



Nervous System 



Eye 



Ear 



Externally 26 

 to 27 myotomes. 

 Inanteriortrunk 

 region muscle 

 plate and cutis 



plate further 

 dififerentiated; 



muscle plate 



extends ven- 

 trally to level of 

 ower margin of 

 notochord. Myo- 

 coele nearly ob- 

 literated. Septa 

 between myo- 

 tomes forming 

 by ingrowing 



mesenchyma. 



Externally 28 



to 29 myotomes 



(?)• 



Extent as above. 



Separated from neural 



tube by mesenchyma 



throughout head and 



trank. Separated from 



gut by mesenchyma 



and dorsal aorta. 



Hypochorda better 



defined. 



Extends to level of ear 

 anteriorly. Separated 

 from neural tube by 

 mesenchyma through- 

 out entire length ex- 

 cept at caudal end. 

 Separated from gut by 

 mesenchyma and dor- 

 sal aorta. 



30 days 

 8 hrs. 



Externally 30 

 to3l myotomes. 



Flexure in mid brain more pro- 

 nounced. Cerebral hemispheres 

 better defined. Neuromeres in 

 medulla well marked. Para- 

 physis indicated as thickening 

 in epithelium. Spinal cord oval 

 in transverse section. Layer ofj 

 fibres well defined in ventro- 

 lateral portion of cord. Spinal 

 ganglia better defined. Many 

 nerve fibers beginning to grow 

 out from ganglion cells. 



Epiphysis better defined; para- 

 physis a slight evagination; 

 walls of both a single layer of 

 cells. Velum transversum also 

 a Single layer of cells. 



Optic cupconcave; Vesiclepear- 

 outer pigment wallj shaped. 

 a Single layer of Ductus endo- 

 cells; inner wall orjlymphaticus 

 retinal layer thick. better devel- 

 Inner ends of cells oped. 



becoming clear. 

 Optic stalk nar- 

 rower. Lens sphe- 

 rical, hollow, not 



completely de- 

 tached from inner 

 layer of ectoderm. 

 Mesoderm extend- 

 ing between lens 



and wall of cup. 



Optic cup more Vesiclepear- 



concave, cavity shaped; 

 very small. Lens lateral por- 

 detachedfromecto-tion of wall 

 jderm ; inner wallthinner,inner 

 thicker than outer. portion thick, 



No cellular ele- Iventral por- 

 ments in cavity ofi tion very 



lens. Mesoderm thick. Ductus 

 also extending be- endolympha- 



tween lens and 

 optic cup. 



Paraphysis a well marked Pigment wall of 

 narrow diverticulum. Spinal optic cup very thin. 



cord cells still arranged radially. 

 Layer of fibers better defined. 



Extends from otic 

 vesicle to fjosterior 

 end of spinal cord. 

 Vacuolated throughout^ 

 greater portion of its 



extent. Separated 

 from neural tube and 

 gut throughout entire 



extent. No mesen- 

 chyma between noto- 

 chord and neural tube. 

 Separated from gut 

 by mesenchyma and 

 dorsal aorta. Hypo- 

 chorda not present(?). 



a Single layer of 

 flat cells. Optic 

 stalk more con- 

 stricted. Lens 

 larger, nearly fiUs 

 optic cup ; cavity 



in lens larger. 

 Mesoderm between 

 lens and ectoderm 

 A few mesoderm 

 ceUs in optic cup 

 behind lens, 



Cervical flexure well marked. 

 Diencephalon and mesence- 

 phalon nearly at right angles 

 to medulla. Velum transversum 

 much deeper. Infundibulum and 

 hypophysis larger, also optic 

 chiasma and torus. Commis- 

 sure in torus recognizable. No 

 plexus. Diencephalon still pro- 

 jects in front of prosence- 

 phalon. Ganglion oftrigeminal 

 very large. Peripheral laj'er of 

 fibers developed in ventral and 

 lateral wall of mid brain. Be- 

 ginning of plica rhombomes- 

 encephalica. Spinal cord oval 

 in section , compressed late- 

 rally ; canal a narrow slit. 

 Spinal ganglia large, well de- 

 veloped. 



ticus bemg 

 constricted. 



Optic cup has outer 



margin in close 

 contact with ecto- 

 derm. Cavity ob 

 literated except at 

 outer margin. Pig- 

 ment wall and re- 

 tinal layer as above. 



Lumen of optic 

 stalk smaller. Cho- 

 roidal groove deep 

 Walls of lens of 

 uniform thickness. 



Vesicle flat- 

 tened on 

 mesial sur- 

 face; walls of 

 saccular por- 

 tion notably 

 thicker than 

 remaining 



portion. 

 Mesoderm 

 separates ve- 

 sicle from 

 ectoderm, 

 also from 

 hind brain. 

 Ductus lon- 

 ger, con- 

 stricted. 



