Normentafeln zur Entwicklungsgeschichte der Wirbelthiere. 
Table 
No. 
| Age 
Urogenital System 
Heart and Blood Vessels 
1 l 
| 12), | 
A small isolated epithelial tube, well cephalad of Wolffian duct, similar to 
| days | 
structure described in 11?),-day embryo. Wolffian ridges quite prominent. 
Wolffian duct on lateral aspect ofridge. Wolffian tubules disappear in region 
|of hind limbs. Cephalad Wolffian duct ends blindly in mesenchyma in region 
‚of fore limbs; duct extends a little farther cephalad than tubules. Ureter, 
|longer, opens into Wolffian duct near entrance of latter into cloaca. Wolffian 
‚ ducts enter cloaca a little anterior to opening of gut into latter, hence be- 
ginning of urogenital sinus. Glomeruli of Wolffian body well formed. 
| 
IR 
| Wolffian ridges very prominent. Epithelium in different parts of Wolffian tubule 
| of different character. Ureter much longer, branched at end into two parts. Con- 
| densed mesoderm around ends. Urogenitalsinus of larger extentthan at 12?/, days. 
Genital ridges small. A few primitive sex cells present. Small genital tubercle. 
| Cephalic end of Wolffian body in region of liver, caudad of fore limbs. 
| Wolffian bodies prominent; they do not extend to region of hind limbs. 
Ureter opens into Wolffian duct just before entrance of latter into urogenital 
sinus. Beginning of tubules in renal anlage surrounded by condensed meso- 
derm. Genital tubercle quite prominent. Urogenital sinus expanded along 
janal aspect of genital tubercle closed by epithelium. Epithelium connects 
urogenital sinus and rectum. Small suprarenal anlage? Genital gland an- 
lage. A few primitive sex cells present. 
Müllerian ducts present; lie on coelomic side of Wolffian ducts; extend only 
a short distance; open into coelom in cephalic part of Wolffian body. 
Cephalad Wolffian duct ends blindly close to Müllerian duct. Ureter springs 
from lateral side of Wolffian duct just before latter enters urogenital sinus. 
Renal anlage contains tubules, is somewhat circular in cross section; its 
cephalic end dorsal to stomach region. Thick collection of cells near cephalic 
|end of Wolffian body, well cephalad of renal anlage, is suprarenal anlage? 
| Genital gland distinct. Urogenital sinus separated from rectum. 
Müllerian ducts open into coelom on median and dorsal aspect of cephalic 
end of Wolffian body. Wolffian ducts form prominent ridges in posterior 
part of coelom. Ureters open into urogenital sinus a little above openings 
of Wolffian ducts. Regions of bladder and urethra indicated in urogenital 
sinus. Numerous tubules in kidney, especially in its periphery. Well marked 
suprarenal anlage. Sexual gland prominent, differentiated as testis (). 
Müllerian ducts extend toward caudal ends of Wolffian bodies. Ureters open 
into urogenital sinus (bladder) some distance above openings of Wolffian 
ducts into same (or urethra). Wolffian ducts lie in beginning of genital cord. 
| Ureters cross to outer side of Wolffian ducts to get dorsal to latter. Kidney 
larger in cross section than Wolffian body; very early beginning formation 
of BOwMan’s capsule and glomerulus in kidney. Sexual cords in sexual 
gland; differentiated as testis (?). 
Müllerian ducts extend toward caudal ends of Wolffian bodies, ending in 
ridges of Wolffian ducts, where they lie on median side of latter. Pelvis 
|of kidney beginning to be differentiated. Glomeruli and BOwMAn’s capsules 
still small. Well marked suprarenal anlage. Distinct sexual cords in sexual 
gland. 
| Caudal ends of Müllerian ducts in ridges of Wolffian ducts, on median side 
of latter. The cephalic portion of Müllerian duct lies on external side of 
Wolffian duct. Glomeruli of kidney more distinct than before. Convoluted 
|tubules beginning to appear in kidney. Differentiation in suprarenal into 
|cortical and medullary regions. Urogenital sinus (vestibule) open in only 
one or two sections. Sexual gland. 
Caudal ends of Müllerian ducts fused, with a single cavity, in genital cord, 
between Wolffian ducts. Numerous glomeruli, convoluted tubules in kidney. 
Cortical and medullary regions clearly differentiated in suprarenal. Wolffian 
body still larger than genital gland. "The latter has a rather slender attach- 
ment to Wolffian body. Genital gland has numerous sexual cords, con- 
taining many primitive sex cells. 
Sinus venosus less prominent than before. Left duct of CuVvIER appears to 
run more to right side of heart. Endocardial cushions project into atrio- 
ventricular canal. Beginning of septum ventriculorum. Trabeculae in walls 
of ventricles more distinet. Cavity of cephalic part of truncus arteriosus 
nearly obliterated by growth of walls. Second aortic arches have disappeared. 
Third aortic arches join dorsal carotids. Dorsal aortic trunks betwen 3rd 
and 4th aortic arches, especially near 3rd arches, very small. : 4th and sth 
pairs of aortic arches. Small pulmonary arteries. Left umbilical vein larger 
than right. Single vitelline vein. 
| Opening of sinus venosus into right auricle has a valve. Left duct of CUVIER 
opens on right side into sinus, which is small. Auricles divided by a septum 
but not throughout. Interventricular septum well advanced. Interventricular 
foramen. Truncus arteriosus in part divided into pulmonary and systemic 
aortae. 5th aortic arches still complete; right smaller than left, however. 
Pulmonary arteries come from their respective pulmonary arches. 4th aortic 
arches large vessels, left a little larger than right. Dorsal aortic trunks between 
3rd and 4th aortic arches nearly obliterated. Vertebral and basilar arteries. Two 
dorsal aortae fuse a little caudad of larynx. Left umbilical vein very large. 
Septum between auricles of heart, with narrow opening dorsally; foramen 
ovale? Auriculo-ventricular canal divided into two parts. Narrow interventri- 
cular foramen. Dorsal aortic trunks between 3rd and 4th aortic arches nearly 
obliterated. 4th aortic arches connected with systemic aortic trunk alone (as in 
13-day embryo). Pulmonary and systemic aortae separated. Left pulmonary 
arch large (ductus Botalli), Right pulmonary connecting arch nearly gone. 
Right pulmonary artery now appears as a branch of left pulmonary arch. 
Right and left pulmonary veins. Right umbilical vein, very small, connected 
with left in ventral abdominal wall: the former vessel enters liver. Large 
vein of liver appearing as continuation of left umbilical (ductus venosus). 
Tricuspid and mitral valves indicated. Opening between auricles dorsally 
(foramen ovale?). 4th right aortic arch (brachio-cephalic). 4th left aortic arch 
large. Ductus Botalli large. Right pulmonary artery appears as branch of left 
5th arch, coming off alongside of left pulmonary artery. Right dorsal aortic 
trunk below region of right 5th aortic arch has in the main disappeared; hence 
in this embryo a single true dorsal aorta (adult aortic arch). No longer any 
connection between right pulmonic arch (artery) and right dorsal aortic trunk 
(right subclavian artery). Dorsal aortic trunks between 3rd and 4th aortic arches 
in the main gone. Pulmonary and systemic aortae separated as far as Junction 
with ventricles; here not yet completely so. Right umbilical vein now does 
not enter liver. 
Semilunar valves of systemic and pulmonary aortae clearly indicated. Pul- 
monary aorta now communicates with right ventricle in the main, but still 
a small channel between systemic aorta and right ventricle. Apparently now 
no connection of right umbilical vein with left and no distinct right umbilical 
vein. In auricle of heart, many nucleated blood corpuscles; many non 
nucleated blood globules. 
Systemic aorta now communicates solely with left ventricle; pulmonary aorta 
solely with right. Right and left ventricles completely separated. In auricle 
of heart, many non-nucleated blood globules, in larger proportion than before; 
also many nucleated blood corpuscles. 
Still large numbers of nucleated blood corpuscles. 
Nucleated blood corpuscles still present but in smaller proportion than 
before. 
Non-nucleated blood 
globules in preponderance but nucleated corpuscles 
easily observable. 
