14 



Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 



Stage 



Series 



27 



127 Trans. 



128 Sag. 

 130 Front. 



28 



131 Trans. 



133 Sag. 



134 Front. 



2g 



135 Trans. 



138 Sag. 



139 Front. 



Length 



14 mm 



15 mm 



16 mm 



Age 



32 days 

 10 hrs 



34 days 

 12 hrs. 



36 days 

 16 hrs. 



Trunk of embryo 



straight when 

 viewed from side. 

 Cephalic flexure 

 still pronounced. 

 Neckbend marked. 

 Pronounced ven- 

 tral band in tail at 

 level of posterior 

 limbs. Lateral cur- 

 vature pronounced, 



Yolk elongated, 

 pear-shaped. Flat- 

 tened on dorsal sur- 

 face ; large abdo- 

 minal vein. Con- 

 siderable pigment 

 in trunk. 



Body Form 



Somites 



Externally 31 



to 32 myotomes. 



In anterior 



trunk region 



myotomes much 



elongated 

 dorso-ventrally, 

 extend below 

 level of noto- 

 chord. Muscle 

 plate Covers one 



half distance 

 between noto- 

 chord and ecto- 



derm. Cutis 

 plate recogniz- 

 able. Septawell 

 differentiated, 

 fibrillae fiU one 

 half of muscle 

 cell. 



Shows 32—34 

 myotomes. 



Trunk and tail 

 straight line. Neck 

 and cephalic flex- 

 ures less pronoun- 

 ced. Tail greatly 



widened dorso- 

 ventrally at level 

 of posterior limbs. 

 Yolk mucli elong- 

 ated, ventral sur- 

 face convex, dorsal 

 slightly concave in 

 profile view. Man- 

 dibular arches 

 strongly devel- 

 oped, ventral ends 

 enlarged , not yet 

 united. Pigment 

 present in trunk 

 and dorsal portion 

 of head. Anterior 



limb buds pro- 

 minent, posterior 

 shght elevations. 



Horizontal 

 section shows 

 36-38 myo- 

 tomes. In 

 anterior trunk 

 region muscle 

 plate extended 

 ventrally to 

 level of pro- 

 nephric ducts. 

 Cutis plate 

 obscure. 



Notochord 



Nervous System 



mesenchyma inter 

 vening. 



Anterior end close 



to hj'pophysis, 

 äome mesenchyma 

 intervening; poste- 

 rior reaches end of 

 spinal cord. An- 

 terior end slightly 

 enlarged. Yolkab- 

 sorbed in central 



portion. Caudal 

 end still in contact 

 with neutral tube. 

 Sheath better de- 

 veloped, not seg- 



mented. Hypo- 

 chorda not present. 



Extends almost to 

 hypophysis, some 

 mesenchyma inter- 

 vening. Knobbed 



at anterior end. 

 Greatest diameter 

 at level of anterior 



margin of yolk. 

 Vacuolated 

 throughout except 

 near ends. In head 

 and trunk consider- 

 able mesenchyma 

 between notochord 

 and neural tube. 

 Sheath better de- 

 veloped. Mesen- 

 chymal thickenings 

 in sheath indicate 

 beginnings of 

 intervertebral 

 disks. 



Eye 



Extent as above. Epiphysis a small flattened 

 Anterior end al- jvesicle; cavity in stalk ob- 

 most in contact 'literated. Posterior commis- 

 with hypophysis, asure indicated. Lumen in 

 small tract of optic stalk very small. Dor- 

 sal wall of diencephalon a 

 Single layer of cells. Para- 

 physis and epiphysis both 

 surrounded bj' mesench^'ma. 

 Plica rhombomesencephalica 

 a deep invagination. Infun- 

 dibulum larger; ventral pro- 



cess extending caudad, 

 posterior wall single laj'er 

 of cells, closely applied to 

 antero-ventral wall of me- 

 dulla. Cord oval in outline 

 in cross section, ventral half 

 narrower than dorsal. Layer 

 of fibers on outside ot ven- 

 tral half well defined. Yolk 

 granules have nearly dis- 

 appeared. 



Velum transversum a single 

 layer of cells. Beginning 

 of choroid plexuses as two 

 invaginations, one in front 

 of paraphysis, other behind 

 it. Posterior and anterior 

 commissure appear. Infun^ 

 dibulum extended laterally 

 Commissura habenularis 

 forming. 



Walls of telencephalon dif- 

 ferentiated into three layers, 

 an outer fibrous layer, a 

 niiddle laj'er of loose cells, 

 and an inner layer of more 

 compact cells. Chiasmacon 

 tains few fibers. Paraphysis 

 widely open, pear-shaped, 

 some lateral diverticula. An- 

 terior and posterior choroid 

 plexuses formed. Posterior 

 larger and more convoluted. 

 Anterior and posterior com- 

 missures present. Anlage of 



cummissura habenularis. 

 Recessus lateralis small ; 

 dorsal, lateral and median 

 longitudinal zones well de- 

 fined. Tuberculum |>o.sterius 

 formed; contains commis- 

 sure 



Margins of optic 

 cup are in close 

 contact with ecto- 

 derm. Wall of re- 

 tina thicker at bot- 

 tom of cup, thinner 

 at margin. Pigment 

 layer thinner, con- 

 sisting of a single 

 layer of flat cells. 

 Optic stalks longer, 

 diameter smaller, 

 lumen still present. 

 Choroidal fissure 

 present. Inner wall 

 of lens thicker than 

 outer, projecting 

 into disk-like 

 cavity. 



Margin of optic cup 

 more constricted. 

 Cavity of optic ve 

 siele still present in 



margin of cup 

 Optic stalk smaller, 

 longer, communi- 

 cates with third 

 ventricle by very 



narrow Channel. 

 Lens more com 

 pletely fills optic 

 cup ; outer wall a 

 Single layer of cells; 

 inner wall much 

 thickened. Mesen^ 

 chyma increasing 

 between lens and 

 ectoderm. A few 

 scattering mesen 

 chyma cells in optic 



cup. Choroidal 



fissure nearly 



closed. 



Ear 



Optic cup more 

 constricted at 

 margin coming in 

 contact with lens. 

 Retina much thick- 

 ened excepting at 

 margin where it is 



abruptl}' tliinned 

 indicating ora ser- 

 rata. Pigment be- 

 ginning to be for- 

 med in retina. 

 Clearzone in retina 

 next to vitreous. 

 Indications of eye 

 muscles. 



Vesicle further 



flattened on 

 mesial surface 

 and elongated 

 antero-posteri- 

 orly. Ductus 

 elongated, nar- 

 rowed and more 

 constricted at 

 base; extends 

 well up on sides 



of medulla. 



External wall a 



Single layer of 



flattened cells; 



mesial wall 



thinner. 



Beginnings of 



lagenaandsemi- 

 circular canals. 



