38 
Normentafeln zur Entwicklungsgeschichte der Wirbeltıere. 
Urogenital System 
Heart, Pericardium, Blood Vessels 
27 
28 
29 
30 
31 
32 
Wolffian duct opens into body cavity at level 
of anterior end of pancreas, is preceded by 
long shallow groove. Extreme posterior end 
solid, fused with lateral wall of posterior part 
of cloaca. Forty-one pairs of mesonephric 
tubules — the first four rudimentary. Posterior 
tubules extend outward and upward over dorsal 
surface of Wolffian duct. Expanded at their 
distal ends and in contact, but not fused, with 
dorsal wall of duct. Interrenal organ as in 
preceding stage (No. 26). 209 germ cells in 
genital region (Woops). 
Wolffian duct opens into coelom anteriorly 
in mid stomach region. Two distinct folds 
in somatic mesoderm below this opening. 
Ducts fused together, and with dorsal wall 
of cloaca at posterior ends. Thirty-eight 
mesonephric tubules, anterior two rudimentary. 
All tubules, except anterior two, connected 
with Wolffian duct. All except anterior two 
tubules dilated before joining duct to form 
Malpighian corpuscle —no glomeruli. Anterior 
part of interrenal organ made up of anasto- 
mosing cords of cells among sinusoids of 
cardinal veins; re organ as in pre- 
ceding stages (No. 27). Genital ridges extend 
from level of first to level of sixth turn of 
spiral valve. In largest part 75 u high, 60 u 
broad at base. 
Thirty-five mesonephric tubules on left side, 
first two and last being rudimentary and not 
connected with Wolffian duct. Glomeruli 
present on all except rudimentary tubules, 
rudimentary on third and fourth tubules. 
Anterior nephrotomes are set at an oblique 
angle to longitudinal axis of body. The pos- 
terior ones lie transversely. The hindmost 
tubules show development ot accessory ureters, 
“Nebenharnleitern”. Müllerian ducts open an- 
teriorly into body cavity on sides of septum 
transversum about one half way ventrally, 
much reduced in size posteriorly, join Wolffian 
duct between Isth and I6th tubules. Posterior 
ends of Wolffian ducts turn sharply downward 
and fuse together over cloaca. Interrenalorgan 
made up of a loose meshed syncytium. Genital 
folds 60 u. high, 75 u broad. 
Thirty-seven mesonephric tubules, first four 
and last two rudimentary. Müllerian ducts 
open anteriorly into body cavity on wall of 
septum transversum, near median line and 
ventral border. Müllerian duct separate from 
Wolffian duct anterior to the seventeenth 
mesonephric tubule. Wolffian ducts communi- 
cate RE for 30 u. Genital folds ex- 
tend from region of closed oesophagus to the 
twenty-sixth mesonephric tubule, i. e., just 
posterior to spiral valve; longest in region of 
stomach. 496 germ cells in genital ridge 
(Woops). Interrenal organ as in preceding stage. 
Thirty-six well developed mesonephric tubules, 
posterior ones open into Wolffian duct by 
short accessory ureters, “Nebenharnleitern”, 
Müllerian ducts meet at ostium, which is 
located in median line of septum transversum. 
Müllerian and Wolffian ducts join between 
thirtieth and thirty-first mesonephric tubules. 
The fused posterior ends of Wolffian ducts 
form a decided swelling on dorsal wall of 
cloaca, but do not open into it. 7IO germ 
cells in genital ridge (Woops). 
posteriorly. 
Walls of both atrium and ventricle much thicker than in preceding stage. Atrium lies mainly over much 
expanded bulbus. Anlagen of valves of bulbus, three mesenchymal thickenings of endothelial lining at level 
of tip of dorsal extension of pericardium. Atrio-ventricular valves represented by slight thickening of endothelial 
wall of atrio-ventricular canal. Anterior part of pericardial cavity, which receives stalks of premandibular and 
hyoid cavities, is connected with cavity proper only by a pair of solid mesothelial cords. — Six complete 
aortic arches in sagittal series (H.E.C. 203). Sixth arch not complete in transverse series. Formation of efferent 
vessels from anterior five arches (H.E.C. 204). Ventral aorta bifurcates at origin of third arch. First arch much 
reduced in caliber at its base. — Vena capitis lateralis nearly equal in caliber to V. cap. mesialis. Extends 
forward beyond otocyst, and communicates with V. cap. mesialis by branches passing between branchial rami 
of vagus, between vagus and glossopharyngeal, between glossopharyngeal and otocyst, and, finally, in front ot 
otocyst. Lateral veins open into common cardinals just above sinus venosus — can be traced backward for a 
few sections only. 
Walls of ventricle and bulbus considerably thickened. Many muscle fibrils in all heart chambers — not cross- 
striated. Dorsal surface of bulbus is fused with floor of atrium anteriorly. Valves of bulbus meet centrally, 
their edges are a little thickened. Atrio-ventricular valves thickened at their free edges. — Lumen of first 
aortic arch completely occluded at its base. Connections of afferent portions of third, fourth, and fifth arches 
reduced to impervious cords. Dorsal aortae between second and third arches reduced to minute vessels, about 
one-fourth caliber of aortae, posterior and anterior to this segment. Vertebral, lieno-gastric, and posterior 
mesenteric arteries developed. — Anterior cardinal vein extends forward to glossopharyngeal nerve. Connected 
with vena capitis medialis by two vessels — one immediately anterior to common cardinal and one at level of 
first spino-occipital ganglion. Vena capitis medialis united ‘with anterior cardinal at level of second spino- 
occipital ganglion. Extends forward to trigeminal ganglion, where it unites with V. cap. lateralis. V. cap. 
lateralis much larger than V. cap. medialis. Lateral vein opens into sinus venosus just below common 
cardinal. Extends posteriorly to pelvic fin. Receives vein from pectoral fin. Jugular vein opens into sinus 
venosus with lateral vein — extends forward to thyreoid. Vertebrals dilated over dorsal surface of Wolffian 
body. A small vessel (lateral mesonephric vein) extends along the base of the lateral surface of the Wolffian 
body. It communicates with posterior cardinal in front of first Wolffian tubule, and with caudal vein 
posteriorly. 
Walls of ventricle and bulbus much thickened with numerous sinusoids, walls of atrium as before. Numerous 
muscle fibrils, none of which appear to be cross-striated. Pericardial cavity completely cut off from the coelom 
ventrally by the septum transversum. Dorsal openings into the coelom are still large. Peritoneal-pericardial 
canal as broad as oesophagus above it, 220 u in length (by sections). — Afferent and efferent branchial arches 
completely separated. Occluded processes of afferent vessels extend dorsally, but do not connect with efferent 
vessels. — Vena capitis lateralis forms main anterior continuation of anterior cardinal. V. cap. mesialis re- 
presented by a few small chambers which communicate with V. cap. lateralis. Orbital sinus as in preceding 
embryo. Posterior cardinal veins arise by bifurcation of caudal at level of 27th mesonephric tubule. Lateral 
mesonephric veins larger than in preceding embryo. Open into ventral surface of caudal vein, posterior to the 
35th (last) mesonephric tubule. Do not communicate with cardinals directly in Wolffian body, but are connected 
by large vessels with the enlarged bases of the segmental veins. Anterior to Ist mesonephric tubule, lateral 
mesonephric veins open directly into posterior cardinals. — Corpuscles broadly oval to round, flatly convex, 
about 20 » in diameter. Nucleus stains darkly, but is not homogeneous. 
Walls of atrium a little thicker than in preceding stage (No. 29). Fibrils in all chambers of heart cross-striated. 
Pericardial-peritoneal canal 0.25 mm. in length (by sections), connecting plate forming posteriorly. — Segmental 
veins dilated over dorsal surface of Wolffian body — from these dilatations vessels pass to posterior cardıinal and 
lateral mesonephric veins. In some places, dilatations of two or three successive segmental veins, connected 
by narrow longitudinal channels. Lateral mesonephric veins open anteriorly into posterior cardinals in front of 
first mesonephric tubule; open into caudal vein by several channels posteriorly. 
Ventricle much enlarged; muscle arranged in distinct trabeculae. Peritoneal-pericardial canal approximately 
0.3 mm. in length (by sections), constricted posteriorly by connecting plate. — Continuous dorsal mesonephric 
vein, formed by fusion of dilated bases of segmental veins.. Communicates with cardinals by main channels 
above glomeruli. Small sinusoids throughout Wolffian body, dorsal to glomeruli*). Lateral mesonephric vein 
anteriorly small and indistinct; posteriorly enlarged, receiving vessels from dorsal mesonephric, and broadly 
connected with caudal vein. — Corpuscles flatly biconvex, roundly oval in outline, 20—25 u in diameter, Nucleus 
densely reticular. 
Ventricle trabeculae much more compactly arranged, ventricle much larger. Peritoneal-pericardial canal approxi- 
mately 0.5 mm. in length — opens on ventral surface of the anterior part of stomach. Very much reduced in 
calibre posteriorly by further fusion of connecting plate. — Dorsal mesonephric veins larger than in preceding 
stage — broadly connected with posterior cardinals by sinusoids. Lateral mesonephric veins small and indistinct 
anteriorly; enlarged posteriorly, and connected by broad channels with dorsal mesonephric veins. Broadly 
connected with caudal vein posteriorly. Cardinal sinus an irregular vascular chamber, Iying above radix 
mesenterica}; communicating by broad channels with posterior cardinals of either side; receives genital vein 
.") The vessel to which the purely topographic term “dorsal mesonephric” vein has been applied, arises, 
as described, by a fusion of the bases ‘of the segmental veins. It corresponds in position, however, to the 
posterior cardinal of mammals. The vessel which arises first in Acamthias, and which has been termed the 
posterior cardinal vein because of this origin, occupies the position of and probably corresponds with the sub- 
cardinal of mammals. 
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