20 



Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 



Stage 



Series 



Length 



37 



192 Trans. 



196 Sag. 



197 Front. 



38 



198 Trans. 



199 Sag. 



200 Front. 



24 mm 



Age 



58 days 



Body Form 



25 mm 



61 days 



Somites 



Notochord 



Nervous System 



Flexures as In anterior 

 above, yolk trunk region 

 elongated, dia-j myotomes 

 meter reduced wider occu- 

 dorso-ventrally pying four 



Anterior end in con- 

 tact with parasphe- 



noid but does not 

 reach level of hypo- 

 physis. Constrictions 



opposite bases of 

 neural arches more 



marked anteriorly. 

 Ossification well 

 marked around sheath. 

 Haemal arches appro- 

 ximating ventrally in 

 tail. Anlage of lateral 

 basal process in carti- 

 lage in anterior por- 

 tion of body. 



Paraphysis with many 



lateral diverticula; still 



opens into third ventricle 



Eminentia Pallii medialis 



well defined, also corpus 



striatum (?). Pallium and 



subpallium differentiated 



Septum ependymale 



present. Beginning of 



taenia fornicis. 



and laterally. 

 Tail broader, 

 less pointed. 

 Surface more 



fifths of 

 Space be- 

 tween noto- 

 chord and 



deeply pigmen-skin; exten- 

 ted;bandsmore ded ven- 

 marked. Roth trally to 



anterior and lower margin 

 posterior limbs of j'olk. 



possess four Myoblasts in 

 digits. Pigment upper por- 



bands more tion of myo- 

 sharply defined. tome com- 

 pletely filled 

 withfibrillae. 



Eye 



39 



201 Trans. 



204 Sag. 



205 Front. 



26 mm 



64 days 

 4 hrs. 



In anterior portion 

 much compressed late- 



rall}', more com- 

 pressed at bases of 

 neural processes. At 

 level of anterior limbs 



smaller than spinal 

 cord; in trunk region 

 and at level of pos 

 terior limbs large as 



cord; in tail about 

 twice the diameter of 

 cord. Yolk all absor- 

 bed. Haemal arches 

 well developed, free 

 ends coalesced. Ossi- 

 fication very consider- 

 able in neural arches 



and notochordal 

 sheath. Lateral basal 

 processes better de- 

 veloped throughout 

 trunk region. 



Compressed dorso- All divisions of brain 

 ventrally in anterior clearly defined. Plexuses 



Ear 



Ductus endo- 

 lymphaticus 

 extends over 

 dorso-lateral 

 walls of me- 

 dulla;stalkvery 

 narrow but still 

 widelyopeninto 

 sacculus. Semi- 

 circular canals 



better devel- 

 oped ; all parti- 

 ally enclosed in 



cartilage. 

 Lagena a more 

 extended evagi- 

 nation. Anlagen 

 of pars neglecta 

 and macula 

 acustica neg- 

 lecta. Macula 

 acustica sacculi 

 two layers of 

 cells thick. 



part of body, laterally 

 in posterior part. 

 Anterior end sur- 

 rounded by hone. 



extending from hemi 

 spheres tomeduUa. Optic 

 nerves verj' small, hollow 

 near brain. Mid brain 



Short, slightly arched. 

 Ganglia habenulae large, 

 symmetrical. Velum 

 transversum contains 

 numerous large blood 

 vessels. Infundibulum 

 wider than mid brain. 



Cerebellum extremely 

 small. Spinal cord oval 

 in section. White matter 

 on outside thickest in 

 lateral portions. Dorsal 

 colunins large, broader 

 anteriorly. Central canal 

 very small nearh' circular 

 in section. Some yolk 

 granules still present in 

 cells of cord. Pia mater 

 well developed. 



Eye not so much flattened 

 laterall}'. Retina shows 

 la\'er of rods and cones, 

 outer nuclear layer, outer 

 reticular layer, inner re- 

 ticular layer, ganglionic 

 layer. External limiting 

 membrane well defined. 

 Choroid better differen- 

 tiated; pigment layer 

 closely apposed to pig- 

 mented layer of retina. 



Lens spherical, sur- 

 rounded by a capsule of a 

 isingle layer of flattened 

 cells. Fibers well devel- 

 joped. No nuclei in center. 

 Posterior Chamber con- 

 tains a few mesenchymal 

 cells. Corneal epithelium 



in two layers. Eye 

 muscles weil developed. 



